Dennis Rader is one of the most sadistic serial killers of all time. He called himself BTK, which stands for 'Bind, Torture, Kill' and he's serving ten consecutive life sentences for his unthinkable crimes. In the past few weeks, police, along with Rader's daughter, Kerri Rawson, have said they are now investigating a further five possible victims linked to Rader with the possibility of more cold cases being looked at.