What makes people go wrong?

The TED presentation below shows the same psychologist Zimbardo. This time he speaks on whether people are bad themselves, or bad behavior also may be caused by the circumstances or the system. this video is specially interesting for people working in prisons.
Beware: shocking images are shown in this video.
Impact has developed a system for positive behavioral influencing of inmates by prison staff, which results from eg Zimbardo’s investigation. If you want you can click for English subtitles: bottom left of the video screen. The video takes about 20 minutes.