What was happening in his prison? People weren't supposed to just die of heart failure when they were young, strong and healthy. The instincts that had helped him when he fought in the war told him that something was not right in his prison.
There was no rational explanation of everything happening but perhaps there was a reason for the lack of explanation? He had seen something like that before, thinks you didn't talk about...
He needed somebody who knew about these things who could help him. He just needed to find the number of his old buddy John Winchester