The LAPD used new DNA techniques to link the Grim Sleeper to various murders through his son's DNA who was in custody. Apparently they did not have Lonnie David Franklin Jr.'s DNA, but his son was a match therefore that meant that the father, the Grim Sleeper was the suspect.
Watch 2010 press conference:
http://www.streetgangs.com/features/070810_grim_sleeper_franklin
Watch 2010 press conference:
http://www.streetgangs.com/features/070810_grim_sleeper_franklin