After eluding a police dragnet for nearly two days, the 33-year-old janitor wanted in the slaying of WMAL radio advertising saleswoman Kathleen Boyden turned himself in yesterday to District of Columbia homicide detectives.

The janitor, David I. Garris of 1812 Vernon St. NW, walked into the homicide squad room at the city's Indianna Avenue police headquarters accompanied by his lawyer and gave himself up to detective Pat Roberts at 9:30 a.m.

Boyden's nude and decaying body was found in the back of her 1980 Toyota shortly after 1 p.m. Tuesday in the 3400 block of 17th street NW in the Mount Pleasant area of the city. City medical examiners said she had been bludgeoned to death.

Police had been looking for her since last Friday when a former roommate who still had a key to her apartment went up there after Boyden, who had a reputation for reliability, failed to report to work.

Boyden was not there, and neither was her car, which she usually kept in the building's basement parking lot.

Several hours later, police entered Boyden's apartment and found that someone had tried to wash away traces of blood from one of the walls. Blood-stains also were found on a stairwell leading to the garage. Police said there was no sign of forced entry at the apartment and that if she was attacked inside, her assailant apparently had a key.

Police said Wednesday that Garris, who was employed at Boyden's apartment building at 3040 Idaho Ave. NW, had been interviewed there several times by detectives while Boyden still was considered a missing person. They said, however, that they had no evidence to justify issuance of a warrant charging him in the murder until late Tuesday night.

Police yesterday would not reveal what that evidence was. They also said Garris had served time in prison after a conviction of violating the Mann Act, which forbids transporting women across state lines for immoral purposes. a

D.C. Superior Court Judge Paul McArdle subsequently ordered the suspect held overnight without bond. McArdle said he would decide today whether to consider a request for bail.