Scotland Yard has denied that its officers have a “licence to kill” after the dismissal of misconduct charges against five officers involved in an incident that led to the death of a black musician.

Marcia Rigg, whose brother Sean died in Brixton police station 10 years ago, criticised the decision of the misconduct panel on Friday. Its decision came despite an inquest ruling in 2012 that the way he had been restrained “more than minimally” contributed to his death.

“Today’s decision and the fact that somebody can be restrained in the prone position for seven minutes has given the officers a licence to kill,” she said.

Assistant commissioner Helen Ball denied claims the panel’s ruling allowed officers to act without repercussions. Responding to Marcia Rigg’s criticism, she said: “Not at all, no of course officers do not act with impunity and there’s certainly no licence to kill, that would be wholly wrong.”

Metropolitan police constables Andrew Birks, Richard Glasson, Matthew Forward and Mark Harratt, and Sgt Paul White had faced disciplinary proceedings over the death of Rigg, 40, at a police station in 2008.

Rigg had been in the grip of a mental health crisis in 2008 and was behaving erratically, aiming karate kicks at passersby in south London, when police were called. He was restrained by officers and taken to Brixton police station, where he died.

The officers were accused of failing to identify and treat Rigg as mentally ill, excessive use of restraint and giving false evidence to the Independent Police Complaints Commission (IPCC) and an inquest into Rigg’s death.

After six weeks of hearings at the Met’s administrative centre in Hammersmith, however, Commander Julian Bennett said: “The decision of the panel is that none of the allegations are proved.”

Marcia Rigg said: “I do not accept this as an honest judgment of the evidence before the panel. I had little faith in these proceedings, but I always held hope that in the end they would do the right thing, based on such clear facts and evidence.

“My question remains, if the police acted as they were required, why is my brother dead? Nothing will tell me that this is justice.”

Rigg’s sister has campaigned for nearly 11 years to get to the truth of what happened to her brother. “It’s been traumatic, sleepless nights, anger, re-living the death at various stages in these 10-and-a-half years that no family should have to go through,” she said.

Deborah Coles, the director of Inquest, which supports the families of people who die in custody, said the system had again failed to hold police to account. “This shameful outcome points to the impunity of the police, and a process which frustrates the prevention of abuse of power and ill treatment,” she said.

The investigations have taken so long that Birks is now an ordained priest, although he is still paid a police salary because he was denied permission to resign while proceedings were ongoing.

An initial hearing by the IPCC exonerated officers of responsibility for Rigg’s death, but in 2012 an inquest jury found Rigg had died of cardiac arrest after “unnecessary” and “unsuitable” restraint while lying face down. This prompted the police watchdog to review its earlier investigation.

It was another four years before prosecutors confirmed that no criminal charges would be brought over his death, bar one count of perjury against White, who was later cleared. The IPCC was abolished in January 2018 and replaced by the Independent Office for Police Conduct, which directed the Met to bring disciplinary action against the officers.

At the beginning of the hearing, Gerard Boyle QC, opening the case for the Met, accused all the officers of failing in their responsibility to ensure Rigg’s safety, four of them of lying to investigators and an inquest jury to hide the truth, and three of them of excessive force.

Boyle said the officers failed to spot signs that Rigg was having a mental health crisis and that they should have taken him to hospital rather than the police station.

In mid-February, however, a number of the charges were thrown out. Claims that Harratt, Glasson and Forward lied about Rigg “spinning” around in the back of the police van collapsed after the panel found the evidence against the officers was “extremely tenuous”.

An expert witness who was asked to make a 3D animation of a figure in the back of a police van initially concluded it was highly unlikely that Rigg would have moved in the way described, but he changed his conclusion when shown a video of Forward moving that way and told the hearing the software used was not meant for forensic purposes.

A pathologist who had been due to give evidence was unable to appear in person for cross-examination so his account was ruled inadmissible.

Another witness, Insp Andrew Dunn, refused to give verbal evidence to the panel in protest at how long it had taken to bring proceedings. He referred lawyers to his written statement and even refused to say whether he recognised himself in CCTV footage from the station on the night Rigg died.

The panel also found no case to answer for a separate count against Harratt over an alleged failure to check Rigg’s passport details on the police national computer.

Ball, the Met’s head of professional standards, said the officers had faced “the most challenging of situations” on the day Rigg died. She extended her sympathies to his family, noting that the officers involved had faced “significant and protracted scrutiny” of their actions.

As a result of Rigg’s case, all police vans are now equipped with CCTV,” Ball said. “I would like to reassure Mr Rigg’s family that over the 10 and a half years since he died, the way in which the Met would respond to someone experiencing a mental health crisis has fundamentally changed. ”

Sarah Green, the regional director of the IOPC, said it was important to independently investigate the actions of the officers involved in the incident that led to Rigg’s death, and for their accounts of it to be tested by a disciplinary panel.