Tariq Jahan says he has lost faith in justice system after IPCC report on police conduct in failed prosecution of eight suspects

A man who was hailed a hero for calling for peace after his son was killed during the 2011 riots has said that police incompetence let the killers walk free.

Tariq Jahan said he had been left devastated and would continue his fight for justice after an official report accused police of being reckless but said no officer would be disciplined.

Eight men accused of murdering Jahan's son and two other men during riots in Birmingham were acquitted in 2012. The lead police investigator was accused by the trial judge of lying under oath, sparking an investigation by the Independent Police Complaints Commission.

The IPCC said one officer who it said had promised witnesses immunity from prosecution in return for their testimony had a case to answer for gross misconduct and had been reckless. But it said the officer, DI Khalid Kiyani, had retired from the police service and could no longer face disciplinary proceedings.

During the trial, Kiyani said his boss, DCI Anthony Tagg, had approved of the offer of immunity, but Tagg denied this. Tagg was accused by the judge of lying under oath, but the IPCC said Tagg had no case to answer. "This investigation did not find any intent to deceive on the part of DCI Tagg in respect of his evidence provided at crown court," it said.

Brothers Shazad Ali, 30, and Abdul Musavir, 31, and their friend Haroon Jahan, 21, were killed as they guarded their businesses in Winson Green, Birmingham, during riots that were part of a series of disturbances across England in 2011. They were flung three metres into the air after being hit from behind by a speeding car.

The acquittals of the eight accused caused anger. Jahan told the Guardian: "I believe the police are responsible for letting the killers get away due to their incompetence."

He said he had believed in the police but had now lost faith in them. "I actually believed in the police and the system. I believed I would get justice and we have waited three years – and then we find the police have been negligent and committed gross misconduct and that leaves me feeling devastated."

Jahan said he believed Kiyani had been made a scapegoat and had made offers of immunity to potential witnesses when other officers were present. "It seems strange that he is a rogue officer, he had 30 years' experience," he said. "There seems to be a cover-up here."

He claimed new witnesses to the police conduct had come forward and had not been interviewed by the IPCC investigators. Jahan said he wanted to meet the home secretary to discuss failings in the justice system, and was considering a European court case.

After his son's death Jahan made an eloquent plea for peace, which was credited with stopping the violence escalating. On Wednesday he said: "I wanted justice, not just a pat on the back … I feel very let down by the people I had faith in, they have devastated my life."

The Crown Prosecution Service decided last year that no officer should face criminal charges.

Gary Cann, assistant chief constable of West Midlands police, said: "The independent investigation shows that no officer from West Midlands police deliberately misled the trial at Birmingham crown court.

"The report recommends that the force reminds DCI Tagg of his SIO [senior investigating officer] responsibilities through management intervention. This has been completed. The force has already taken steps to strengthen some of the procedures we have with other criminal justice partners. The learning from this investigation has been built into future training for all senior investigating officers."