Regarding your question about what approach the defense will take -
Because he stated he had never met Sierra, there's no way defense can discount the DNA black fiber evidence, saying it was from prior meeting.
His lie about his never having met her seals his fate as far as I'm concerned.
I'm sure his defense will try to change that, but there's only one version of the truth, while as we all know, a lie had many versions.
I'm trying to think of ways the defense could explain it.
They would almost certainly have to concede that Garcia-Torres was in contact with Sierra at some point, although it'd hurt his credibility in the jurors' eyes (since it means he lied to the police).
Sierra's DNA in his car - and his DNA and fibers on Sierra's stuff - could be explained in a few ways:
1. Cross-contamination, whether deliberately or through police incompetence.
2. If they argue that Sierra's a runaway, they could make up a story about her flagging down Garcia-Torres and hitchhiking to ... somewhere. That would explain her DNA in his car.
The rope:
1. The real abductor/killer discarded the rope. Garcia-Torres stumbled across it on his way to the reservoirs and decided to take it for later use, not knowing it was used in a crime.
2. This depends on whether his car lets you reach the trunk if you're sitting in the backseat. My hair's very long; it's only inches away from reaching my tailbone and I
hate the feeling of a stray strand brushing up against my arm. I'll sometimes run my fingers through my hair to removed any loose/unattached strands. They could say that Sierra, who was sitting in the back seat, did this and dropped the strand behind her and into the trunk, where it flitted down and fell on the rope.
They could claim that the semen explanation Garcia-Torres gave was innocent.
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They could go with ''Yes, my client was with Sierra when she died, but it was an accident and he just panicked and hid the body'', or ''He kidnapped Sierra but she died accidentally'', or ''Sierra hitchhiked to (city) and Garcia-Torres didn't tell the police because he didn't want to get her in trouble''.