At least four police officers - including the Area Commander for Mid-South Canterbury - are under investigation in relation to false evidence in court.

The Independent Police Conduct Authority has found the use of the taser against Timaru man Troy Reuben was excessive, and that two officers involved knowingly lied while giving evidence in court.

It also found the Police Prosecutor failed in his duty to ensure correct evidence was permitted in court - and he was potentially told to go ahead by Inspector Dave Gaskin.

Assistant Commissioner Allan Boreham says the investigations are wide ranging.

"We're doing an inquiry which will look at all the actions of all the people involved whether it's people who gave evidence or people who gave them advice on that evidence."