Ian Tomlinson is likely to have died from injuries sustained when he was pushed from behind by a police officer at the G20 protests in London, a forensic pathologist told an inquest.

Dr Nat Cary conducted his postmortem a few days after video footage showed PC Simon Harwood striking Tomlinson with a baton and pushing him to the ground near the Bank of England two years ago. Tomlinson, 47, collapsed and died less than three minutes later.

Cary said he believed the way Tomlinson fell to the ground was likely to cause a "blunt force trauma" to his abdomen. He said damage to the liver was the "most likely" cause of the internal bleeding, but the blood loss could have been caused by other burst veins. He believed this led to rapid internal bleeding, which would have caused Tomlinson to collapse to the ground and go into cardiac arrest.

The video footage showed Tomlinson was unable to properly break his fall, he said, and his elbow became trapped between his body and the pavement. Bruises on the outside of his body, and those to his abdomen, were consistent with this.

Cary's findings contradict those of another pathologist, Dr Freddy Patel, who was the first to examine Tomlinson's body. Two other pathologists, Dr Kenneth Shorrock and Dr Ben Swift, have concluded that the newspaper seller died of internal bleeding.

Earlier in the week, Patel said he spent hours looking for a cause of the internal bleeding but, when he could not find a source, concluded through a "process of elimination" that Tomlinson died of natural causes. He specifically concluded that Tomlinson, a father of nine, died from sudden "arrhythmic" heart attack caused by coronary artery disease. He accepted that a heart attack may have been triggered by Tomlinson's encounter with the police officer 150 seconds earlier, conceding there was a "compelling association" between the two incidents.

Whereas Patel believed Tomlinson's most blocked coronary artery was 80% to 90% blocked, a body tissue expert said that the same artery was 50% blocked. Cary's opinion was that the same artery was between 60% and 70% blocked, which he said was very unlikely to have triggered a heart attack. "This is not the sort of blockage in atheroclerotic disease in coronary arteries that causes sudden death," he said.

A pivotal element within the inquest is the extent to which three litres of fluid found in Tomlinson's abdomen consisted of blood. Patel was the only pathologist to observe the fluid, which he described as "a large-volume intra-abdominal bleed".

However 12 months later, after reading how other pathologists had found Tomlinson died of internal bleeding in the abdomen, Patel changed his description to "[bodily] fluid with blood".

Patel told the inquest he did not know what proportion was blood but believed it was mostly bodily fluid. He said a sample he took of the fluid was inadvertently discarded.

Cary told the jury that he could not be sure from photographs of the amount of blood. But he added that despite Patel's altered findings he was confident the quantity of blood in the abdomen was "substantial" and enough to cause Tomlinson's collapse and subsequent death.

"Clearly at the time Dr Patel took that sample, he must have thought that a significant proportion of it was blood, because he was going to submit it for toxicology as blood."

• Ian Tomlinson inquest: all Friday's developments