Solving crime with forensic linguistics

Dr John Olsson talks to Michael Rosen about how he uses forensic linguistics, specifically authorship analysis, to solve crimes including murder, false witness and hate mail. What he does is work out whether a text, email or letter is likely to have come from the person it says it is from - or whether, in some cases, it is in fact being sent by the person who has murdered them.. Producer Beth O'Dea