I think that TOBY is the Scranton Strangler because of many reasons.
First of all, he was absent on the day the Scranton Strangler chase was on TV in the office. When the office was watching it at his desk, his phone rang, and Kelly immediately hung it up. His car is also the same car as the one on the news. Second of all, when he went to visit George Howard Skub in prison, I think that he told Skub that he was the REAL Scranton Strangler, and that's why he got strangled. And finally, think about it: Why would Toby care so much about the Scranton Strangler case, other than the fact that HE was the real Strangler?