They're called crimes of passion, the sort of crimes where true love turns into obsession, betrayal and revenge. Former NSW rugby union representative Paul Mulvihill claimed he was trying to defend himself when he stabbed his ex-lover in 2012 after she broke off their affair. But it was no accident. There's also the case of Allison Baden-Clay, reported as missing by her husband who was later charged with her murder. So often there is a thin line between the one you love and the one you murder.