A state appeals court has overturned the conviction of a Los Angeles man found guilty of killing a 17-year-old girl and her 16-year-old brother, ruling that the judge in his trial admitted improper evidence.

City News Service says the 2nd District Court of Appeal ruled Monday that a judge wrongly allowed evidence that one of Williams' alibi witnesses was arrested in possession of a gun used in the killings.

The court said the evidence was prejudicial and the trial court abused its discretion.

A jury found Williams guilty of the 2004 killing of Shulma and Jason Ramos, and he was sentenced to life without parole.

Prosecutors said the teenagers were looking for a party with friends when a group of gang members that included Williams fired at their car.