In February 2016 Mark was given his own crime strand on ITV's This Morning. Unsolved took a closer look at undetected crime.
His first three cases were the murders of Jill Dando, Claudia Lawrence and the disappearance of the Malaysian flight MH370.
His first Unsolved case was the murder on the 25th April 1999 of TV Presenter Jill Dando, who was killed by a single shot to the head on the doorstep of her Fulham home.
Watch: Who killed Jill Dando?
Watch: Where is Claudia Lawrence?
Watch: Where is Madeleine McCann?
Watch: What happened to flight MH370?