A convicted serial killer has been found guilty of three additional murders during the "Southside Slayer" attacks that terrorized Los Angeles in the 1980s and `90s.

Court clerk Lynnie Reeser says a jury on Thursday convicted Michael Hughes of first-degree murder with special circumstances. Prosecutors will seek the death penalty when the sentencing phase of trial begins Monday.

Hughes was found guilty of strangling two prostitutes and a 15-year-old girl. Authorities say DNA evidence linked Hughes to the killings, which occurred between 1986 and 1993.

The former security guard already is serving a life sentence for killing four women in the early 1990s.

Hughes was investigated by a task force looking into the killings of as many as 90 women in inner-city Los Angeles. Several killers were later convicted.