williams wasn't on trial for the murder of mark hasse or mike mclelland. murder of cynthia mclelland. >> not guilty, your honor. >> reporter: why not just try the murders at the same time? >> what if something went wrong in the first trial? we wanted to have the ability to be able to try him twice and make sure he got justice. >> reporter: christina sat in court and had to relive the deaths of her parents. what gave you the strength to go to court every day? >> i showed up every day for the three people who gave their lives for something good. they stood up. and they did what they were supposed to. and they died for it. >> this is my chance to tell you story of the murders of mike and cynthia mclelland. >> reporter: prosecutor bill wirskeye thought if he could prove eric williams had killed cynthia, that would obviously show he killed mike. >> you'll hear the story of a massive law enforcement investigation -- state, local federal agencies working together to build an air tight case. >> reporter: one of the first witnesses called -- cj tomlinson, dallas pol