I hope the prosecution does have good evidence. Depending on what kind of DNA they found and what other circumstantial evidence (esp. surveillance) they have, the outcome might not be certain. It wouldn't take a criminal (or attorney's) mastermind to come up with a story where he just drives through the area, stops as he sees something lying on the street and finds a bag. He picks it up and takes it in his car, puts in on passenger seat/backseat. He rummages briefly through the contents (depending on what evidence there is, the phone might be inside, too). He then continues on his way to go fishing or whatever, intending to later deliver the bag to police or lost and found or maybe sell some of the stuff on eBay.
However, he learns about the missing girl and realizes that he's in trouble. He has no alibi for hours, was in the immediate area and is in possession of SL's items. He would be immediately suspect, especially considering his arrest record. He panics and dumps the stuff.
Police tracks him down nonetheless, but he realizes that dumping the items made him look even more suspicious, so he denies involvement.
It explains his car on surveillance (assumed they just have his car, not SL clearly inside), his DNA on her clothes, even her DNA in his car (transmitted via bag).
LE had a lot of stuff that the public wasn't aware of, they may have a lot up their sleeves. But if they just got tired and thought that putting some pressure on him would make him talk, and they actually have nothing more than could be explained by a scenario like above, they might really try to stall in the hopes of finding her body (and thus more evidence).
Depending on what evidence they have, there might still be the possibility of him walking.
