A convicted murderer serving a life prison term was charged yesterday in three Anne Arundel County homicide cases, each more than a decade old, after authorities used DNA to link him to the killings, police said.

Alexander Wayne Watson Jr., 34, imprisoned for life without the possibility of parole for a 1994 murder in Prince George's County, was charged with three counts of first-degree murder in the deaths of Mary Elaine Shereika, 37, Lisa Kathleen Haenel, 14, and Boontem Andersen, 34. The slayings occurred between 1986 and 1993.

"Today is a great day for the police department of Anne Arundel County," County Executive Janet S. Owens (D) said at a news conference at police headquarters.

Authorities said Watson was "an associate" of the family Andersen was living with in 1986, but they would not elaborate. They said he was not acquainted with the other victims. Anne Arundel State's Attorney Frank R. Weathersbee said that if the slayings were committed by the same person, as police believe, then "that could make him a serial killer."

Watson, who is imprisoned at the Maryland House of Correction Annex in Jessup, appeared in Anne Arundel District Court yesterday for a bail hearing on the new murder charges. No bail was set, and he did not enter pleas.

Wearing a gray prison jumpsuit, Watson sat quietly beside his attorney and briefly answered Judge Martha F. Rasin's routine queries.

Weathersbee's spokeswoman, Kristin Riggin, said prosecutors have not decided whether to seek capital punishment for Watson, who was convicted in the June 13, 1994, robbery and killing of office manager Debra Cobb in Forestville.

Anne Arundel Police Chief P. Thomas Shanahan credited the new charges against Watson to the persistence of the department's cold-case squad and to advancements in DNA technology. "DNA is the most exciting thing that happened to law enforcement since fingerprinting," Shanahan said.

"It's a tremendous relief," said Shereika's daughter, Jennifer Shereika, 33, who lives in southwestern Virginia. "We owed it to our mother to see whoever committed this crime brought to justice."

According to police, Andersen's body was found Oct. 8, 1986, in her home in the Gambrills area of Anne Arundel. She had been sexually assaulted, stabbed and strangled.

On May 23, 1988, Mary Shereika's fiance reported her missing after she failed to return home from a morning jog. Her body was found in a field in Gambrills. She also had been sexually assaulted, stabbed and strangled.

On Jan. 15, 1993, Haenel's mother reported her missing after she did not show up at Old Mill High School, where she was a freshman. The next day, the boyfriend of Haenel's mother found the girl's body in woods behind the school. She had been stabbed and strangled.

Homicide Sgt. David Waltemeyer said that when investigators were analyzing the "solvability" of various cold cases in 1998, the three cases were selected for close scrutiny partly because DNA had been recovered in each.

Although the DNA samples had been previously tested, detectives wanted to retest them using newer technology and enter them in databases not available a decade ago, said Jeff Cover, supervisor of the department's crime scene unit.

In the Andersen and Shereika cases, DNA had been obtained with vaginal swabs. In the Haenel case, DNA was recovered from a Newport cigarette near her body. Police said they determined that traces of Haenel's blood and Watson's saliva were on the cigarette, a brand that Watson was known to have smoked.

The DNA profiles were entered into state and federal DNA databases. Watson's DNA profile already was in the databases because he is a convicted violent felon. Last fall, detectives learned that a match had been made linking him to the Shereika and Haenel cases.

Police said they also learned that in 1986 and 1988, Watson lived in Gambrills, close to Shereika and Andersen. In 1993, he lived in Glen Burnie, close to Haenel, police said.

"They made sure this case was not locked away in a file cabinet somewhere," Weathersbee said. "DNA is a timeless stamp that can always be used as evidence."

Alexander Wayne Watson Jr. is charged with three homicides committed in Anne Arundel.Mary Elaine Shereika, 37, went for a morning jog in 1988 and later was found dead in a field in Gambrills.Lisa Kathleen Haenel, 14, failed to show up at school in 1993 and was found dead in nearby woods. Boontem Andersen, 34, was found slain in her home in 1986. She had been raped, stabbed and strangled.