Ian Tomlinson's family react to the verdict. Source: guardian.co.uk guardian.co.uk

Britain's most senior prosecutor has said he was considering whether to prosecute the police officer who attacked Ian Tomlinson for manslaughter after an inquest jury found that the newspaper seller had been unlawfully killed.

Tomlinson, 47, had been trying to walk home from work through the G20 demonstrations near the Bank of England when he was attacked from behind by a Metropolitan police constable, Simon Harwood, a member of the Met's Territorial Support Group (TSG).

Returning their verdict after three hours of deliberation on Tuesday, jurors said Tomlinson died of internal bleeding in the abdomen after being struck with a baton and pushed to the ground with "excessive and unreasonable" force on 7.20pm on 1 April 2009.

Within minutes of the verdict being announced, the director of public prosecutions, Keir Starmer, said a "thorough review" of his earlier decision not to bring criminal prosecutions against Harwood had begun.

"That review will now take place and will be thorough," he said. "It will take into account all of the evidence now available, including any new evidence that emerged at the inquest, the issues left by the coroner to the jury and the conclusions they reached. The review will be conducted as quickly as is compatible with the care and rigour required in a thorough exercise."

For legal reasons, the jury's verdict could not name Harwood or apportion blame. The verdict, however, did say that Tomlinson's death came after he was "fatally injured. This was as a result of a baton strike from behind and a push in the back by a police officer which caused Mr Tomlinson to fall heavily," the verdict said. "Both the baton strike and the push were excessive and unreasonable. As a result, Mr Tomlinson suffered internal bleeding which led to his collapse within a few minutes and his subsequent death."

Their finding noted Tomlinson, a father of nine, was walking away from police, obeying orders and posed "no threat" when he was struck by Harwood.

There were shouts of "yes" from Tomlinson's family when the verdict was returned.

His son Paul King said afterwards: "We've got a long way ahead of us. We've been let down for two years. It's been proven that Ian was killed unlawfully. Now we'd like to go to court and continue with the manslaughter charges."

The Met expressed "profound condolences" to Tomlinson's family, saying in a statement: "It is a matter of deep regret that the actions of an MPS officer have been found to have caused the death of a member of the public."

The Tomlinson inquest verdict comes just over a year after the Met was forced to accept one of its officers almost certainly killed Blair Peach, an anti-fascist protester, at a protest in Southall, west London, in 1979.

The Met kept a report into Peach's death secret for more than 30 years. It revealed he was killed by an officer from the Special Patrol Group – the precursor to the TSG.

Police initially denied Tomlinson had had contact with police officers before his death. Reporters were briefed that Tomlinson had died of "natural causes".

Tomlinson's family, who have alleged that police covered up information about involvement in his death, were told he probably died of a heart attack before a postmortem had even taken place.

They were discouraged from talking to reporters investigating the death and told Tomlinson has simply been seen to "run out of batteries".

Details about a bruise on his leg and puncture marks in his skin, now known to have been caused by a baton strike and dog bite, were also withheld from them.

However, the release six days later of footage obtained by the Guardian showing the newspaper seller's encounter with Harwood prompted the Independent Police Complaints Commission (IPCC) to launch a criminal inquiry.

The footage was played repeatedly during the five-week hearing at the International Dispute Resolution Centre in Fleet Street, London. Starmer said last July he did not believe a prosecution was possible because of complications on medical evidence, which he said meant prosecutors would struggle to prove a cause of death.

There were two divergent explanations of Tomlinson's death.

The first pathologist to conduct a postmortem examination on the body, Dr Freddy Patel, said he died of a heart attack as a result of coronary heart disease. He was contradicted by three other pathologists who examined Tomlinson's body, all of whom found he died of internal bleeding in the abdomen.

Starmer said last year that changes in Patel's evidence about the extent of blood found in Tomlinson's abdomen rendered any prosecution particularly difficult.

However, Patel made several changes to his evidence in the course of the inquest, and was undermined by a number of experts, including a heart specialist who said defibrillator readings showing Tomlinson's heart attack were "entirely inconsistent" with Patel's theory.

The jury was also told that Patel had twice been suspended by the General Medical Council disciplinary panel in recent months after being found guilty of a botched postmortem and dishonesty.

Reviewing his decision, Starmer will have to consider the new medical evidence as well as the jury verdict.

The jury had to be satisfied "beyond reasonable doubt" that Tomlinson's injuries were caused by the trauma of the fall – the same standard of proof that would be applied in a criminal trial.

Starmer's initial decision not to prosecute was backed by the attorney general, Dominic Grieve, but prompted widespread anger and questions in parliament. The Met commissioner, Sir Paul Stephenson, said at the time he could understand the "outrage" over the decision not to prosecute Harwood. The IPCC is also known to have believed there was sufficient evidence to bring a manslaughter charge.

In a statement released through his lawyers on Tuesday, Harwood said he was "sorry" Tomlinson died, but denied he intended to hurt him.

"The mass of video and other evidence gathered by the IPCC now presents a picture very different from the one PC Harwood had on the day," his lawyer said. "In particular, he wishes that he had known then all that he now knows about Mr Tomlinson's movements and fragile state of health."

• This article was amended on 4 May 2011. A sentence in the original read: The jury had to be satisfied "beyond reasonable doubt" ... the same burden of proof that would be applied in a criminal trial. This has been corrected.