EXPERTS probing the death of Irish revolutionary Michael Collins have concluded he was shot with a rifle from higher ground, ruling out a conspiracy theory that he was killed by one of his own men.

A century after Collins was killed in an ambush in rural Cork, forensic scientists and historians have re-investigated his murder.

The research team, led by the Republic's former state pathologist Marie Cassidy, say "it is highly likely" an exit wound on Collins head was mistaken for an entry wound.

Professor Cassidy also says Collins "died from a gunshot injury to his head....consistent with a rifled weapon".

The manner of Collins' death in August 1922 in Béal na mBláth has led to a century of speculation and remains one of the most contentious events in Irish history.

Drawing heavily on historical scholarship and verified witness testimony, a new RTÉ documentary 'Cold Case Collins' sees Professor Cassidy chair a 21st century cold case where the experts curate evidence and artefacts with modern day scientific analysis about the death of Collins.

Much of the evidence focuses on the wound found on the back of his head, but Professor Cassidy is drawn to testimonies about an entry wound found above his left ear, that appears to have been missed.

"The body was then taken up to Dublin and the doctor, Dr Gogarty, was the person who was asked to embalm the body and he also mentioned this large wound at the back of the head," said Professor Cassidy.

"But we have a matron, Eleanor Gordon, and a commandant Frank Friel, and they both talk about an entry wound on the hairline as well as the exit wound at the back of the body.

"I'm beginning to lean towards that being the most accurate.

"When the bullet strikes....it's a very narrow point that actually strikes it, so the entry wounds are often tiny, they're often missed in the initial examination because they're so small and there's blood everywhere."

Asked if she believed the exit wound had been mistaken for an entry wound, Professor Collins said "I think it is highly likely"

"What we have heard today is that a bullet has gone through the front and come out the back," she said.

Asked about the theory he had been killed by one of his own men, Emmet Dalton, amid speculation that he was shot from behind from close range, Professor Cassidy said she did not believe that to be the case as it "would have left a contact injury which would be fairly sizeable".

Concluding, Professor Cassidy said "in my opinion he died from a gunshot injury to his head and that is consistent with a rifled weapon and the entry wound would have been somewhere around and above the left ear and that the bullet took a tangencial path across the back of the head to exit on the right side".

"We have clear evidence that this was a rifle gun shot wound, that he was most likely shot by someone who was standing above, firing down at him and unfortunately caused his death."

Cold Case Collins is RTÉ One tonight at 9.35pm and on the RTÉ Player.