The police officer suspended following the death of Ian Tomlinson during the G20 protests has been questioned on suspicion of manslaughter after a second postmortem examination showed the newspaper vendor did not die of a heart attack.

The findings released today show Tomlinson, who was thrown to the ground by a Met officer during the protests, died from an abdominal haemorrhage.

The dramatic shift led the Independent Police Complaints Commission to confirm that the officer under investigation in connection with the alleged assault had been questioned about manslaughter.

Tomlinson's family believe today's findings make a manslaughter charge against the officer more likely. His son Paul King said: "First we were told that there had been no contact with the police, then we were told that he died of a heart attack; now we know that he was violently assaulted by a police officer and died from internal bleeding. As time goes on we hope that the full truth about how Ian died will be made known."

Tomlinson, 47, collapsed and died moments after being attacked from behind by a Metropolitan police territorial support group (TSG) officer on 1 April at about 7.20pm. The constable, whose identifying badge number was not on display, has not been identified.

He had been trying to make his way home from work when he was confronted by police, hit with a baton and thrown to the ground. Initially, police said he had previously had no contact with the police, and alleged that medics were impeded from helping him as "a number of missiles – believed to be bottles – were being thrown at them".

A couple of days later, the Guardian published a photograph of him lying at the feet of police officers, along with the testimony of three witnesses who described him being hit with a baton or thrown to the ground by police. The IPCC criticised the Guardian for upsetting Tomlinson's family and briefed other journalists that there was "nothing in the story" that he had been assaulted by an officer.

It was only when video footage emerged that the officer responsible was suspended and a criminal inquiry launched.

An initial postmortem, by the Home Office pathologist Dr Freddy Patel, found that Tomlinson died after suffering a heart attack. But Dr Nat Cary, the pathologist who carried out a second postmortem at the request of the IPCC and Tomlinson's family, concluded that while there was evidence Tomlinson suffered hardening of the arteries in his heart, it was not serious enough to kill him.

Jules Carey, of Tuckers, the solicitor representing Tomlinson's family, said today that "the video footage of the unprovoked and vicious assault on Ian by the police officer would easily justify charges of assault being brought against the officer. The findings of Dr Nat Cary significantly increase the likelihood that the officer will now face the more serious charge of manslaughter."

He said the family had been aware of the findings of the second pathology report for a week and had been forced to endure "continuing reports in the press that Ian died of a heart attack".

Carey added: "The IPCC opposed the disclosure of Dr Cary's findings until they satisfied themselves that it would not prejudice their investigation of the officer. It is of some comfort to the family that the record is now being put straight, but they hope that the IPCC investigation will be expedited and thorough, and that there will be a prompt referral to the CPS for charge."

A statement from the City of London coroners court said: "Dr Cary's opinion is that the cause of death was abdominal haemorrhage. The cause of the haemorrhage remains to be ascertained. Dr Cary accepts that there is evidence of coronary atherosclerosis but states that in his opinion its nature and extent is unlikely to have contributed to the cause of death."

The IPCC has previously said CCTV footage showed Tomlinson walking up King William Street after 7pm and approaching one of several police cordons opposite the Bank of England.

Denis O'Connor, the chief inspector of constabulary, who will carry out the review, said this week he would examine all aspects of the Met's public order policing, including techniques such as kettling – the containment of thousands of protesters inside police cordons for hours at a time.

O'Connor has been called in by the Met commissioner, Sir Paul Stephenson, who said the move had been prompted by concern over policing of the G20 protests. The Met will scour its own surveillance footage of the demonstrations in the City of London to search for further evidence of police misconduct.