David I. Garris, convicted slayer of Kathleen Boyden, an advertising sales representative for radio station WMAL, was sentenced yesterday by a D.C. Superior Court judge to a prison term of 27 years to life.

Garris, 33, of 1812 Vernon St. NW, was convicted last Dec. 19 of a charge of first-degree murder and six other charges, including robbery and grand larceny, in Boyden's slaying. Her nude and decomposing body was found Sept. 23 in the rear of her car, which was parked in the Mount Pleasant section of the city.

Throughout his trial, Garris, who worked as a janitor in the apartment building where the victim lived, contended that he was innocent. He said he had visited friends and various bars the night Boyden was killed before he went home from work.

Garris continued to maintain his innocence at yesterday's sentencing, telling Judge Fred B. Ugast that he had access to documentation that would prove his innocence.

Assistant U.S. Attorney Richard C. Otto, who prosecuted the case, asked Ugast to sentence Garris to maximum terms. Ugast sentenced Garris to 20 years to life for first-degree murder and consecutive sentences of 5 to 15 years for robbery and 2 to 6 years for larceny of Boyden's car. Garris must serve 27 years before he is eligible for parole, according to his lawyer, Christopher G. Hoge.

Garris also was given concurrent sentences of 20 years to life for felony murder; 3 to 9 years for grand larceny of Boyden's property, and 15 to 45 months for unauthorized use of Boyden's car.

Boyden was last seen alive the night of Sept. 17 when she returned to her apartment building on Idaho Ave NW.

Moments earlier, according to a desk clerk who testified at the trial, Garris had picked up a set of Boyden's keys.