The Independent Police Complaints Commission has widened its investigation into contacts police and other agencies had with a disabled Iranian refugee murdered by a vigilante who wrongly believed him to be a paedophile.

Bijan Ebrahimi, 44, had complained to police after suffering antisocial behaviour but was killed two days after he himself was arrested after completely unfounded complaints that he had a sexual interest in children. Following the murder, his body was set on fire.

The IPCC has been focusing on the days leading up to the murder in Bristol last July.

But on Sunday night it announced it was widening the investigation and looking at how Ebrahimi was treated by Avon and Somerset police over a number of years.

It will also look at how the force worked with other agencies who had dealings with Ebrahimi after his arrival in Britain in 2000.

The events of July were not the first time he had been the subject of apparent hate crime. He was forced to move out of a previous home after it was set on fire.

The IPCC commissioner, Jan Williams, said: "The evidence has dictated that we must look at the force's policy and approach to these sorts of incidents and complaints and any potential organisational failings that Avon and Somerset need to deal with."

Three police constables have been interviewed under caution for the potential offence of misconduct in a public office.

They are the two constables who attended Ebrahimi's home on the day he was arrested for suspected breach of the peace and another constable who was made aware of issues regarding him next day.

The IPCC is planning to make a further appeal for information about his arrest later this month.

Lee James, 24, who admitted murdering Ebrahimi, was jailed for life in November and told he will serve at least 18 years in prison for what the sentencing judge, Mr Justice Simon, called an "act of murderous injustice".