Half an hour before midnight, the streets of Baltimore were deserted and the temperature had dropped below freezing. Assistant U.S. Attorney Jonathan P. Luna paused for the security barricades to open and then turned his silver Honda from the federal courthouse garage onto Hanover Street.

It had been a long day, followed by a late night. After negotiating into the dinner hour over guilty pleas in a heroin-trafficking case, Luna had gone home to Howard County, but returned to his office nearly three hours later to wrap up the legal paperwork. He was due in court at 9:30 the next morning to conclude the drug case after three days of trial in U.S. District Court.

Luna departed again. But instead of heading south toward the townhouse he shared with his wife and two young sons, he joined the stream of 18-wheelers and late-night travelers driving north on Interstate 95.

By 1 a.m., he had crossed into Delaware. Two hours later, he was on the Pennsylvania Turnpike, heading west.

A few hours after that, the 38-year-old prosecutor's body was found in a tiny creek in Pennsylvania Dutch country. Still attired in a business suit, overcoat and tie, his electronic security pass fixed around his neck, he had been stabbed and pricked 36 times with a knife.

His Accord, idling nearby at the edge of the creek near a well-drilling business, was smeared with blood. Across the road, a woman was just beginning to milk her family's cows.

More than two weeks later, the largest team of investigators assembled since last year's sniper attacks has yet to fathom the curious late-night mission that carried Luna through three states and ended with his death in Lancaster County.

It has been an investigation with few leads and many theories. As investigators have pursued them, those theories also have been spun out in popular Internet chat rooms and by the armchair detectives on cable news talk shows.

The early theorists suggested that it was retribution by the seedy sorts whom Luna prosecuted -- drug dealers and consumers of child pornography. But as the slender details of the crime began to emerge, speculation shifted to an encounter of a personal nature. Those details suggested that he had rushed off to meet someone he knew. But whom?

In an electronic age, it seemed likely that cell phone records or e-mails or the vast network of surveillance cameras would lead swiftly to the killer. Investigators pored over telephone records, bank and credit card accounts and the contents of Luna's computer and electronic Palm Pilot organizer as they worked to retrace his steps. Pennsylvania State Police returned to the creek off Dry Tavern Road where his body was found, combing the area with metal detectors.

Investigators puzzled over a credit card debt that Luna had run up without his wife's knowledge, found that someone using his name had posted ads on the Internet several years ago seeking a discreet relationship with a woman and discovered that Luna had adult pornography stored on his office computer that did not appear to be directly related to the porn cases he handled.

And, investigators said, they learned that Luna made several earlier trips to Lancaster County that no one seemed able to explain.

Cash, Gas and Video

The big rest stop on I-95 in Delaware, just outside Newark, is a modest pavilion of food stands bookended by two boldly lighted service stations. By the time Luna passed through that plaza it was 1 a.m. Thursday, and the counters that sell cinnamon buns and burgers, pizza, snacks and souvenirs had closed for the night.

His bank card was popped into one of the two blue Wachovia Bank automated teller machines in the small hexagonal lobby, which is monitored by numerous cameras. Records show a $200 withdrawal. None of the cameras, however, was able to capture a clear picture of the transaction, investigators said.

By Thursday evening, federal agents had arrived at the plaza to question people about Luna, according to an employee, who spoke on condition that her name not be used. The agents returned Friday to collect security camera tapes from Manny Dominguez , manager of the plaza's Exxon gas station.

There's no evidence from that morning that Luna bought gas at the Exxon, but two hours later his credit card was used for a gas purchase at a Sunoco station in King of Prussia, just northwest of Philadelphia. An attendant told investigators Luna was alone when he paid for the gas, but a video camera from the store did not record Luna, and a law-enforcement source said the attendant's description of Luna was a bit inaccurate. The attendant, who has since quit for reasons unrelated to the case, could not be reached to comment. Other attendants declined to comment.

The unexplained late-night foray to Pennsylvania puzzled many of Luna's friends and colleagues, who remember him as a conscientious prosecutor and doting father, a loveable man with a winning smile. A handsome man, his looks were likened to those of Tiger Woods.

He organized the office softball team, ran marathons, loved the New York Yankees and listened to any kind of music from classical to bluegrass to Luther Vandross. Days before Thanksgiving, he joined the Baltimore chapter of the Barristers Club, a group of judges and lawyers.

"I never saw anything that indicated anything but the highest principles," said U.S. District Judge William L. Osteen, who hired Luna as a law clerk years ago.

Reginald Shuford, a staff attorney for the American Civil Liberties Union in New York, said Luna's friends and family have been distressed by speculation over the circumstances leading to his death.

"Jonathan was an honorable and always dignified man," said Shuford, who roomed with Luna while they were students at the University of North Carolina School of Law. Back then, he never knew Luna to have any debts other than student loans, and he never so much as saw Luna with a pornographic magazine. "He was devoted to his family. He was absolutely committed to them and adored them."

The rush judgments by Internet gossips and cable show speculators do not fit the profile of the son of a restaurant steward who pulled himself up from the Bronx, interrupted law school to care for his cancer-stricken father, helped move his parents from New York to Maryland so they would be closer to him, and contributed to the rent on his parents' Columbia townhouse. They don't match the public profile of a young man who gave up his job in the Brooklyn District Attorney's office and moved away from his beloved New York because his wife's large family was from Maryland and because he believed the area was a better place to raise a family.

'He Was Very Courteous'

The Peter J. Camiel Plaza rest stop sits beside the Pennsylvania Turnpike about halfway between Philadelphia and the place where Luna died. In addition to a Roy Rogers, a Sbarro, a TCBY and Starbucks coffee shop, the plaza offers a Sunoco gas station.

Luna had been stopping there for gas and coffee about once a month during the last six months of his life, Carly Caduto said last week. A service station attendant who works the midnight shift for Sunoco, Caduto said she could not recall whether Luna passed through on the night of his death, but she did remember that he always used a credit card if he bought gas and always paid cash if he bought coffee.

They often made small talk, and his dapper attire made him stand out.

"He was very courteous," she said.

Caduto's boyfriend and colleague at the service station, Mark Reilly, said an FBI agent passed through after the slaying. Luna had been seen the night he died at a gas station 23 miles to the east. Had he also been here? asked the agent, who carried a Post-it note with the words "3:26 a.m.," "credit card" and "TPK7" scribbled on it.

By then, investigators already had a rough reconstruction of Luna's movements to that point. After meeting in Baltimore with a defense lawyer about 6 p.m. to work out a plea, Luna promised to draw up the legal papers that night and went home to the townhouse in Elkridge where he lived with his wife, Angela, their sons -- 5-year-old Justin and 10-month-old Jacob -- and his mother-in-law. Luna returned to the federal courthouse on West Lombard Street at 8:48 p.m.

At 9:06 p.m., Luna placed a 10-minute call with his cell phone to one of the defense attorneys, Arcangelo M. Tuminelli. Luna told the lawyer that he needed to go home again but that he planned to return to the office to complete the paperwork.

About 9:30 p.m., Luna left a voice message on the cell phone of attorney Kenneth W. Ravenell, who represented the second defendant in the drug-trafficking case. Once again, Luna said he planned to wrap up the legal paperwork that night and fax copies to Ravenell.

But investigators apparently had learned nothing that could explain why Luna would be driving west on the Pennsylvania Turnpike about six hours later.

His car left the turnpike after 3:30 a.m. at Exit 286, south of Reading. The ticket turned in to the tollbooth worker had a speck of blood, a law enforcement source said, and DNA tests are being conducted to determine whether it was Luna's.

Worries That Linger

Jonathan Luna died in a lonely, ugly place -- a long, shallow creek that winter has turned brown and bare. The tires of his car cut into the cold ground as it swerved off Dry Tavern Road, leaving tracks down to the very edge of the creek in the hours before dawn Dec. 4.

There are a couple of houses in the distance, and the Sensenig and Weaver Well Drilling building is a stone's throw from where the car came to rest.

At about 5:30 a.m., Daniel Gehman, a Sensenig and Weaver employee, was prepping the rigs when he noticed an odd-looking red light glowing in the darkness. He maneuvered a drilling truck's headlights onto the area and saw what he thought was an accident involving a Honda Accord. He called police, who discovered a body in the creek.

In Baltimore, Luna was reported missing after he failed to show up for work. But it wasn't long before the body in the creek was identified as his.

A Sensenig employee named George, who spoke on condition that his last name not be used, said people who live near where Luna's body was found also have their theories on how a man from Baltimore came to be killed in an area where slayings are rare.

"I'm using the theory that he was meeting someone halfway" between Baltimore and the place where he died, George said. He said many residents felt the killer had to have known the area to find the creek from the turnpike.

"You just don't run into this place" by happenstance, George said. "The community's fearful."

Fred Martin, another worker at the well drilling company, said people were baffled by the slaying. "That's the big question: Why here?" Martin said. "It's a complete shock, nothing much really happens around here. It's a big mystery to us."