He knew something was wrong and began doing what he knew best -- research.

CNN: College professor goes from fat to 'Mr. Low Body Fat'

"He was a person of conviction and when he made up his mind about something, right, wrong or otherwise, he made up his mind and you weren't going to convince him otherwise, " Usera said.

CNN: Notorious company: Dorner a 'friendly guy' gone bad

He said he realised something was wrong when he arrived in Washington and Mr Mallon was not there.

BBC: Consultant faces sex charges