article_snippet: Boston (CNN)It was 9:35 on a slow Thursday night in April 2013 and Massachusetts Institute of Technology Police Chief John DiFava was about to call it quits.
article_snippet: dispatcher David Sacco tried to summon Sean Collier on dispatcher David Sacco police radio.
article_snippet: dispatcher David Sacco sent an emergency alert.
article_snippet: dispatcher David Sacco tried texting dispatcher David Sacco.
article_snippet: It became an amount of time that wasn't comfortable," dispatcher David Sacco said.