From what I can tell, "Touch" DNA was found on Sierra's folded clothing that did not belong to Sierra. It was compared against the California data base of convicted felons and they got a "hit" with Torres, who lived only 7 miles away.
They checked out Torres' car and it was the red Jetta. Reviewing available video's, it was found that Torres' car was "in the area" around the time of the abduction. It is unclear how closely they tie him to the abduction site but the videos shoot down any other alibis. He was definitely "in the area".
A forensic examination of the Jetta turned up "touch" DNA that was "probably" Sierra's. A further study of other sex crimes in the area revealed that Torres could be "100%" linked forensically (we don't have the details) to one assault and is the prime suspect in two others.
That is pretty much the case. Good but not Rock Solid. The big problem is "touch" DNA. It is different from the DNA results were are used to based on blood or semen. It can degrade and give results that are far below the "Billion to one" matches we have come to expect. Sometimes there is real controversy as to whether or not the sample is even a match. You sometimes get "dueling expert witnesses" at trials.
"Touch" DNA is best when you get a "blind hit" with someone who is otherwise a good suspect: ties to the crime scene, history of similar crimes etc. The DNA on Sierra's clothing is compelling evidence if Torres has no other explanation how it got there.
The DNA found in the car is much less solid. Apparently there are fewer "matching points and there are quite possibly many people in the general population besides Sierra that could have provided that DNA.
The big question is how solid a case does the DA really have? Finding the body would really help. One possibility would be to drop the charges on Sierra go after him for the sexual assault and get a very long prison sentence. That would buy a little time to investigate the case further. Advances in forensics may work in the prosecution's favor.