Produced by Clare Friedland, Lourdes Aguiar, Elena DiFiore and Shoshanah Wolfson [This story previously aired on July 15, 2017. It was updated on Dec. 29, 2018.] Matt Herren still struggles to make sense of what happened the night of Oct. 12, 2012, when his close friend, Ryan Poston, was killed. "I think about him every day," Herren said. "You don't think something like that is ever going to happen to someone you know." "Is there something I could've done that could've prevented that? And I know a lot of people in his life had to have felt the same way," Herren told "48 Hours" correspondent Peter Van Sant. How did things spiral so out of control between Ryan and his girlfriend, Shayna Hubers, that she shot him to death -- insisting it was to protect herself? "What was lost when your friend was shot and killed?" Van Sant asked Herren. "He's the type of person that you want in your life," he replied. "Not just a friend, but a loving son, a protective, adoring older brother." "He had … [Read more...] about New murder trial for Shayna Hubers: Why did she shoot Ryan Poston six times?