The thing that cinches this case the most for me is the witnesses who saw him talking to her on the trail. I did believe the ones who made eye contact with him, who passed within 6 feet of him while riding by on their bikes. I believe that the eye contact left a strong impression in their minds. I believe that their "gut" told them that something was off about the scene.
I think he may have stalked her. I think he may have seen her out walking her dog before, while he was riding around on his motorcycle through town. I think his postings about getting a girl to like you, etc, were the signs that a fixation on her was developing in his mind.
He had to ride his bike pretty far down the path to where he found her- that makes me think that he knew she would be on an isolated stretch of the trail. Maybe he saw her in the blocks near her house and then drove around to the other end of the trail where he could then approach her on his bike.
Despite the lack of DNA, I just feel very strongly about his guilt in this case. I think he's just lucky that due to the type of attack, it was hard to get much DNA.