Andrew Phillip Cunanan, suspected murderer of Gianni Versace and four other men, appears to change his killing technique in the same way that he has changed his name, his hairstyle, his life history.

Cunanan, the object of a furious manhunt since Versace's broad-daylight slaying in Miami Beach on Tuesday, does not fit the standard profile of a serial killer. Rather, say criminologists, he allegedly is something far more rare, a "spree killer." A spree killer tends to be unpredictable, perhaps not knowing what his next move will be.

"There's no pattern to his killings. That's what makes everybody so nervous," said Jack Levin, a serial murder researcher at Northeastern University in Boston.

If Cunanan is in fact the killer authorities say he is, he has shown no standard "MO" other than leaving a car near his crime scenes. Police say he will sometimes kill savagely, monstrously, like a psychopathic serial killer -- bludgeoning one victim with a claw hammer, apparently torturing another with garden clippers -- and yet he has also killed like a common thief, just to steal a truck. Tuesday, authorities have said, he killed like an assassin, shooting Versace twice in the head at close range.

In all this, the motive is a mystery.

"He's just a horrible monster," said Philip Horne, a San Francisco civil rights lawyer who said he had planned to become roommates with Cunanan this spring.

Serial murder experts have taken to the airwaves since the Versace murder, but there is little consensus about what might be driving Cunanan. Personal revenge? Thirst for publicity? Hatred of his own homosexuality? The tragic tale is further proof that human psychology is an inexact science, that the criminal mind can be elusive and inventive.

"This guy's different," said former FBI serial killer profiler Clint Van Zandt. "We've had homosexual serial killers before, but he's a particular breed."

The typical serial killer works in stealth, often over many years, almost invariably driven by sexual sadism, the murder being part of an elaborate ritualized fantasy that the killer keeps trying to perfect. Serial killers, preferring a more intimate form of violence, rarely use a gun the way Cunanan allegedly has. Some experts have compared Cunanan to Theodore Bundy, because both were charming and intelligent and able to elude capture, but Bundy took few risks, left few clues, and killed as a way of satisfying a violent sexual compulsion.

Robert Ressler, a former FBI serial killer profiler, compared Cunanan to Christopher Wilder, a South Florida serial killer in the 1980s who, when identified, turned into a spree killer, leading authorities on a cross-country chase, opportunistically taking lives, before finally dying in a shootout in New Hampshire. Ressler said Cunanan also brings to mind Charles Starkweather, who killed the family of his 14-year-old girlfriend in the 1950s -- including her baby sister -- when he wasn't allowed to marry her, and then drove across the high plains, stealing cars and shooting people.

But none of these killers, by whatever label, ever did anything as bold, as certain to attract international attention, as Tuesday's murder of Versace. The criminologists can't quite figure it out. The closest parallel may be the Manson family's grisly murder of actress Sharon Tate and several others.

"He's not in a singular pattern. He is able and willing to kill either if he has to, or if he wants to," said James Fox, author of several books on mass murder. "We sometimes eat because we're hungry and we sometimes eat because we like the smell and we sometimes eat because it's dinnertime. Why can't that be true of killers too?"

Lurking behind Cunanan's life story is a lingering problem with identity. According to friends and acquaintances, he made up stories about himself that made him seem glamorous. He claimed to be a millionaire's son. He claimed to be a rich traveling businessman. This spring he told his San Francisco friends that he had purchased a factory in Mexico with 70 employees, and that it made prefabricated movie sets for Hollywood.

"He lied to us all along because he was trying to make himself into something better than what he really believed himself to be," Horne said.

The youngest of four children, Cunanan grew up in San Diego County, attended Bonita Vista Middle School in Chula Vista, then went to the prestigious, private Bishop's School in the beach village of La Jolla. The sedate campus, built in Spanish mission style in 1909, has sand-colored buildings surrounding a quiet quadrangle where students practice lacrosse. He was a good student, ran track and cross-country, and was openly gay. His chosen quote in the yearbook was, "Apres moi, le deluge" -- "After me, the flood."

He would later tell friends that he went to Yale or the U.S. Naval Academy, but in fact he enrolled at the University of California at San Diego. A history major, he dropped out in 1988 just as his father, Modesto Cunanan, became a fugitive. The elder Cunanan reportedly was indicted for fraud after allegedly skimming more than $100,000 from a business deal. He fled to his native country, the Philippines, where police in Plaridel, north of Manila, located him yesterday, the Associated Press reported. He told investigators he does not believe his son killed Versace.

In the early 1990s Andrew Cunanan lived in San Francisco, becoming a fixture on the nightlife circuit. Jesse Cappachione, one of the managers of Midnight Sun, a gay bar on San Francisco's 18th Street, said, "He was gregarious, loud and always wanting to be the center of attention. He threw a lot of money around. Some people thought he bordered on the obnoxious. He was constantly laughing."

Later he moved back to the San Diego area, reenrolled at UCSD, but still didn't graduate. He worked off and on at a Thrifty drugstore in the hometown suburb of Rancho Bernardo. A cashier's job was not to his liking, and so he found a new calling: gigolo. He was not a male prostitute -- as his mother once told reporters -- but rather a kept man, a more or less full-time boyfriend to older, wealthy gay clients.

What he didn't have were close, intimate friends, a lover his own age, someone with whom to share his life on equal footing, according to those who know him. He became estranged from his mother; she lives in nearby National City but now refuses to talk to the press. To hear Cunanan's friends in San Diego and San Francisco tell the story, Cunanan for all his charms did not have lasting and meaningful relationships. He started inventing a history. To friends, he lied about having an ex-wife and a child, he lied about coming from a wealthy family with sugar plantations in the Philippines, and he even lied about his name. He was not "Andy DeSilva," as everyone thought.

Greg Tankersley, a part-time actor and waiter who socialized with Cunanan, said, "He has a gregarious personality, an infectious laugh." But he had no meaningful liaisons, was never seen touching or kissing anyone. "It did seem kind of odd, that he didn't seem interested in anyone," Tankersley said.

Nicole Ramirez-Murray, social editor of the Gay and Lesbian Times, said, "I don't think that Andrew had any real friends."

Cunanan's Hillcrest friends didn't know much about his other life with the wealthy, closeted businessmen of La Jolla. Ramirez-Murray frequently saw Cunanan at social gatherings at the estates and sprawling seaside homes. "To be a gigolo you definitely have to be in tune with what your customer, your sugar daddy wants," he said. "That is, a well-rounded educated man who can -- as Andrew could -- discuss the arts, discuss antiques, wines, best of restaurants, current affairs and politics. He mastered that. He certainly was a man who could hold his own and keep the interest of his elderly gentlemen."

One of Cunanan's patrons was Norman Blachford, a millionaire businessman with a condo in La Jolla, said Lt. Jim Collins, the head of the homicide unit of the San Diego Police Department. Blachford reportedly traveled with Cunanan to Europe and gave him spending money. Blachford, contacted at home Wednesday and Thursday, declined to comment, saying, "I'm not talking to any journalists."

Blachford broke up with Cunanan last year, Collins said, and Cunanan moved from La Jolla to an apartment in trendy Hillcrest. Some friends wondered why he'd live so humbly given what they thought was his wealthy background. In Hillcrest, Cunanan had a near-daily routine of walking Bartley, his roommate's Rottweiler, in the afternoon, then stopping in at Flicks, an upscale gay club, for cranberry juice and a round of "Megatouch" video. He ate at California Cuisine, usually ordered filet mignon, and always picked up the tab for his friends, tipping lavishly, laughing loudly. Waiters would vie to serve his table. Manager George Kalamaris said, "If someone were to tell me a year ago that Andrew Cunanan was a murderer I'd say forget it. He was a gentleman, well-educated."

One nightclub owner said he glimpsed the darker side of Cunanan. Two years ago, Joe Letzkus, the owner of Flicks, got a phone call from a man who identified himself as Andrew DeSilva.

"I'd like to get to know you better. Perhaps we can explore having a relationship," the man said, Letzkus recalled. "I said I didn't know him, I didn't want to know him."

The conversation quickly turned unpleasant, with Letzkus warning Cunanan/DeSilva not to call again, and threatening to alert the police if he did.

Letzkus later realized his caller was one of his customers. The club owner said he never felt comfortable around Cunanan after that. "The way he looked at me was -- pure hatred," said Letzkus. "He would just glare at me. . . . He was frightening. I thought, This guy's an evil person,' like he was demonic almost."

Letzkus, for one, said he is worried that he could be a future target of Cunanan. The whole community is on edge, with rumors that Cunanan might return for a Gay Pride festival next week. His roommate, Erik J. Greenman, has been under FBI protection and so far has declined to be interviewed. Reached at the dingy apartment building where he lived with Cunanan, the compact, muscular, spiky-haired Greenman told The Washington Post, "Now I'm waking up with photographers hanging off my balcony again."

No one knows what caused Cunanan allegedly to turn homicidal. Friends said something obviously had changed in him. He didn't look as good. He had broken up with his latest "sugar daddy," as Ramirez-Murray put it. He ran up $25,000 on his credit cards.

"He let himself go and had not been keeping up his gigolo looks. He realized that his lifestyle and his career as a gigolo was coming to an end. I feel he fell into a rage and then in his warped mind he said, I'll let them know I'm around,' and now he has the attention of the world," Ramirez-Murray said.

Horne, his San Francisco friend, said, "He was one of those guys who definitely peaks between 18 and 21." Cunanan didn't go to the gym. He wasn't fat, exactly, but, "He was like, very soft," Horne said.

Cunanan's friends threw a farewell party for him at California Cuisine on April 24, bringing flowers and candles to the restaurant. The friends, for once, picked up the tab. Cunanan gave away a lot of his personal belongings, expensive shoes and sweaters that he had bought on Rodeo Drive in Los Angeles.

But there was one ominous note at the dinner. At one point, Cunanan reportedly looked around the table and said, "None of you really know who I am."

He said he was heading to San Francisco to live after "taking care of some business" in Minnesota. On Friday, April 25, he arrived in Minneapolis and had drinks with his old boyfriend, David Madson, according to Minneapolis police and news reports. He also hooked up with another close friend from San Diego, Jeffrey Trail.

Collins, the San Diego police homicide lieutenant, said there has been speculation that Madson and Trail had started a relationship, that Cunanan found out and snapped. In any event, that Sunday night a neighbor heard angry shouting in Madson's apartment.

Madson didn't go to work Monday, nor the next day. Police went to Madson's apartment and found a bloody hammer. Then they found, rolled up in a rug, a body, horribly bludgeoned. They assumed it was Madson's corpse, but it was Trail's. Also on the scene was a gym bag with Cunanan's name on it. A .40-caliber handgun was missing from its holster.

"There was very little effort in this case to hide this crime," said Minneapolis police spokeswoman Penny Parrish.

Madson's body turned up four days later, on Saturday, found by two fishermen in the reeds by a lake north of Minneapolis. A different murder, a different murder technique: Madson had been shot three times. His red Jeep had been stolen. Authorities charged Cunanan with second-degree murder. He was clearly on the road, however, and the cops were days behind him.

The next day, May 4, in Chicago, a woman named Marilyn Miglin went home and discovered that her husband, Lee, a real estate magnate, was missing. She called police. They found Miglin in the garage, taped like a mummy with air holes for his nostrils, his throat slashed with a saw, his chest jabbed with pruning shears.

"This is someone who went out of his way to hurt the victims very badly," Van Zandt said.

Lee Miglin, said a family spokesman, was not gay and had no connection to Cunanan.

There have been reports that Cunanan may have known Miglin's son, but the family has insisted the murder was random.

The red Jeep was found nearby. Missing this time was Miglin's Lexus. Cunanan is believed to have driven to New Jersey, allegedly murdered with one shot to the head a cemetery caretaker there, William Reese, and stolen his red pickup truck. The Lexus had been abandoned nearby. Criminologist Ressler said Cunanan may simply have run out of gas and needed a new vehicle.

Cunanan may have gone into New York City. There were reports that he was seen in the Hell's Kitchen area of Manhattan in mid-May, using the DeSilva alias.

Then he may have come to Washington. A man resembling Cunanan was seen at three gay bars on South Capitol Street the evening of May 15. Someone else was said to have seen him that day near Dupont Circle.

Police believe Cunanan then went south. A senior law enforcement official in Miami who asked not to be identified said Friday that Cunanan had been in South Florida for a minimum of 30 days before the Versace murder, and perhaps for as long as two months. He said police and FBI agents have interviewed people who said they had seen Cunanan in locations on South Beach, North Miami Beach, Key West and West Palm Beach, among other places. "We've had a number of sightings, but we haven't confirmed any to our satisfaction," the official said. "It's like so many other things {with this investigation}. We've been a day late and a dollar short."

The official said he didn't believe Cunanan was any kind of criminal mastermind or expert in disguising himself.

"The problem we've had is the guy's so ordinary, average height, average build. You look at the photos of him, and he could be four or five people," he said. "This is not a guy who stands out in a crowd, not someone you'd necessarily notice or remember." Achenbach reported from Washington and Waxman from San Diego. Staff writers Audrey Gillan, Brian Duffy and Linton Weeks in Washington and special correspondents Stephen Levine in San Francisco and Kari Lydersen in Chicago contributed to this report. CAPTION: SLAYINGS LINKED TO CUNANAN The FBI is looking into the possibility that one of its most wanted fugitives, Andrew Cunanan, killed Gianni Versace in Miami Beach Tuesday. Cunanan has been charged in one killing and named as the prime suspect in three others. Minneapolis, April 29 Police discover the bludgeoned body of Jeffrey Trail, 28, rolled in a carpet in the apartment of architect David Madson. The FBI said Trail, a manager at a propane delivery company, and Cunanan were lovers and that Trail knew Madson. Rush City, Minn., May 3 Fishermen find David Madson's body on the edge of a lake north of Minneapolis. He had been shot three times. Police say Madson, 33, and Cunanan were once lovers but that Madson had ended the relationship because he considered Cunanan "shady." Cunanan is charged in Madson's slaying. Chicago, May 4 Body of millionaire real estate developer Lee Miglin, 72, is found stabbed and slashed in the garage next to his town house. The next morning, police discover Madson's red Jeep Cherokee parked near Miglin's home. Miglin's green 1994 Lexus is missing. Pennsville, N.J., May 9 Cemetery caretaker William Reese, 45, is found shot to death near Miglin's Lexus. Reese's red Chevy pickup is missing. Miami Beach, July 15 Fashion designer Gianni Versace, 50, is shot twice in the back of the head outside his oceanfront mansion. Reese's pickup truck is found in a nearby parking garage. SOURCE: Associated Press CAPTION: In Castro District of San Francisco, barber Juan Rivera tapes up "Wanted" poster for Andrew Phillip Cunanan.