Police investigating the Virginia Tech killings are looking at whether Cho Seung-Hui was copying parts of a violent film when he murdered 32 people.

Officers believe he repeatedly watched Oldboy as part of his preparation for the killing spree.

The film, which won the Grand Prix award at the 2004 Cannes film festival, has been described as "an ultra-violent movie of obsession and revenge".

It contains stylised scenes of killings and an attempted suicide, and is filled with what one critic called "punishing emotional violence".