A recent spoiler helps clear up whether or not Michael Mancini really killed Sydney!
So is Michael the Melrose Place killer since he had the bloody necklace in his car? — Sharon Dee
MICKEY: "Someone is going down," says Shaun Sipos, who plays David, the necklace-finder. "If it wasn't for David, the killer would still be at large." Sipos stops short of identifying his TV dad as the killer, emphasizing that while David's motives might be ethically dubious, his heart's in the right place. "He's helping the police because he really cared about Sydney," he says.
Source: TV Guide