. >> reporter: tim lovett was the state's collision reconstruction expert.id the evidence showed frances chased and hit bonnie. >> that escalade definitely hit that range rover at least two, maybe three times. >> reporter: but frances' defense attorneys, leigh cutter and jean brown, said investigators made a big mistake when they bought into the story of bonnie contreras. >> everyone got their information from one person at the scene. and that's bonnie. and bonnie lied her ass off. >> reporter: defense accident reconstructionist charles ruble said there was no physical evidence to back up bonnie's claims that frances had hit her over and over again. no evidence, he said, the suvs had even touched. >> not even once. >> reporter: and remember how bonnie said her purse flew forward off the seat when frances hit her? >> this is her purse in her car. i get hit from the rear. where's my purse go? it doesn't dump in the front. that's simple physics. >> reporter: in fact, he said, the purse falling forward supports frances' claims that bonnie was repeatedly slamming