When there is insufficient evidence or cooperation from the suspect - what’s left for authorities to try to get a conviction? The 'Mr. Big' technique is often a last resort for police to solve a murder. But the elaborate tactic to elicit confessions from suspects is under fire. The technique has become so controversial that some countries have gone as far as to ban the practice. Reporter Jayme Doll delves into a number of high profile cases and examines: how far should undercover police go to catch a killer?