"Significant questions" remain about the behaviour of a police officer who was cleared of the manslaughter of Ian Tomlinson during the G20 protests, the police watchdog said.
The Independent Police Complaints Commission's deputy chairwoman, Deborah Glass, ordered that Pc Simon Harwood will now face Metropolitan Police disciplinary proceedings in public.
A jury of seven women and five men took 18 hours and 45 minutes to clear him.
He cried in the dock and his wife Helen sobbed as the verdicts were given, before they tearfully embraced as he was freed.
Mr Tomlinson's family also broke down, and outside court stepson Paul King called the verdict "a joke", vowing to pursue the issue in the civil courts.
Mr Harwood hit 47-year-old Mr Tomlinson with a baton and pushed him to the ground on the fringes of the G20 protests.
The father-of-nine walked 75 yards before he collapsed, and died later in hospital from internal injuries.
Ms Glass said it was "staggering" that he managed to medically retire from the Met while facing disciplinary proceedings for an alleged road rage incident - and despite this was later re-employed by the force as a police officer specialising in public order.
She said: "While the jury has today acquitted Pc Simon Harwood of manslaughter, it is clear that significant questions remain in connection with his actions on the day Ian Tomlinson died.
"Whether or not those actions were reasonable will be tested further at a misconduct hearing in September, which I have directed will be held in public.
"There are also questions in this case that the Metropolitan Police Service must answer.
"Pc Harwood was able to retire from the Metropolitan Police while facing disciplinary proceedings for previous alleged misconduct towards a member of the public.
"That he was then re-employed by the force, first in a civilian role and later as a constable, is simply staggering and raises considerable concerns about their vetting procedures."
Mr Harwood, from Carshalton in Surrey, said he used reasonable force when he hit Mr Tomlinson with a baton and shoved him to the ground as he walked away from police lines in the City of London.
Mr Tomlinson was an alcoholic and had slept rough for a number of years.
An inquest was held into his death last year, where the jury returned a verdict of unlawful killing.
Speaking outside court today, Mr King said: "After the unlawful killing verdict at the inquest last year, we were expecting to hear a guilty verdict not a not guilty verdict. It really hurts.
"But it's not the end, we're not giving up on justice for Ian.
"There has to be one more formal and final answer to the question 'who killed Ian Tomlinson?' That will now be pursued in the civil courts."
Jules Carey, solicitor for the Tomlinson family, said: "This is one of the hardest days for the family, and there have been many.
"Pc Harwood may have been acquitted of manslaughter by this jury, but another jury, at the inquest a year ago, found that Ian Tomlinson had been unlawfully killed. It is impossible for this family to understand these two, apparently contradictory, verdicts.
"Ian Tomlinson's family have not given up on justice. They will now look to the civil courts to reconcile these verdicts, deliver justice and formally answer the question 'who killed Ian Tomlinson?'"
Metropolitan Police Deputy Assistant Commissioner Maxine de Brunner said the force had done all it could to co-operate with the investigation.
She said: "The evidence has now been put before the jury and they have reached their decision.
"It has always been the intention of the Metropolitan Police Service to hold the misconduct hearing as soon as possible. This was delayed pending the outcome of the trial. Papers were served on Pc Harwood in November 2010 informing him of the intention to proceed to a gross misconduct hearing.
"Following the conclusion of the trial of Pc Harwood, we will now need to review the misconduct case against him, as required by the Home Office guidance."
A group of around 30 demonstrators staged a protest on the pavement outside Scotland Yard's headquarters in central London on Thursday evening.
They shouted "Who killed Ian Tomlinson? The police killed Ian Tomlinson," in unison while cries of "murderers" were also heard.
Some held posters with "Defend the right to protest" emblazoned across them.
Around seven police officers stood and watched as the demonstration went on.
Martin Abrams, 32, from London, said: "1,433 people have died following contact with police since 1990 and zero police officers have been convicted.
"It's as if the police are above the law and I think today's ruling that Pc Simon Harwood has been found not guilty of manslaughter is an absolute travesty.
"There is video evidence of him violently striking and pushing him which was said in court to have caused Ian Tomlinson's death.
"Pc Harwood is a thug, he's got a lot of violent incidents behind him which couldn't be given during the court case - is that fair?
"It could have happened to any one of us. It just so happens that Ian Tomlinson was somewhat down on his luck but that shouldn't prejudice things.
"I'm here today to say this should stop."