andrea canning: tim mcvay's murder trial started in june of 2015. >>> tim mcvay's murder trial startede michael meersman would decide. >> mcvay's defense attorneys believed they held the winning hand. >> he passed the polygraph. so we thought this could be the truly innocent accused here. >> prosecutor john mcgehee knew he was facing a tough test. >> you had no cause of death. you had no weapon. you had no ironclad forensic evidence. >> i did feel that it could be an uphill battle, that it was going to be a real challenge. >> as the trial began, mcgehee presented the prosecution's theory as to how tim did it. >> even though there was no official explanation for how carrie died, the state presented something called, birking a method of suffocation designed to leave no marks by sitting on someone's chest, and covering their nose and mouth. >> to support that scenario, the state called one of mcvay's ex girlfriends, katie smitty. >> why are you nervous? >> i'm scared of him. >> katie described an incident one night in 2013. she said she was startled awake by mcvay sitting on her chest. >>