The BBC has obtained previously unseen footage of a man who died after being restrained by prison officers, which contradicts the version of events put forward by officials.

BBC News took Scottish ministers to court earlier this year after they refused to hand over CCTV footage of the moments leading up to the restraint incident after which Allan Marshall died.

Prison officers had previously claimed the 30-year-old, who was on remand for unpaid fines and breach of the peace, had smashed up his cell and covered himself in excrement.

The new footage shows Marshall, from South Lanarkshire, walking calmly through the prison for four minutes, lightly guided by three guards.

Marshall was on remand at HMP Edinburgh in 2015 when he was restrained face down by up to 17 prison officers. He died four days later.

In evidence to a fatal accident inquiry, officers talked about Marshall behaving erratically and aggressively and their belief he had taken a legal high.

He was being moved to the prison’s segregation unit because of his actions during the night and officers said he needed a shower after a dirty protest.

However, the newly-released footage shows Marshall walking topless through the prison corridors.

He does not appear to be covered in excrement as officers had claimed and he is not behaving erratically as he is led to the shower room.

Footage of the restraint incident, which occurred outside the shower room almost 20 minutes later, has been in the public domain for years.

However, a court case brought by Marshall’s relatives meant new footage of events before the restraint was lodged with the Court of Session.

Despite this, it took months of legal wrangling for the BBC to obtain the footage.

On more than two occasions lawyers for Scottish ministers said the previously seen restraint footage was the only CCTV they had.

A Scottish government spokeswoman said it apologised for the failures that led to Marshall’s death.

“The ongoing legal proceedings mean it is inappropriate to comment further,” she said.

The new footage shows Marshall leaving his cell at 07:25 accompanied by three prison officers.

It shows him coming down several flights of stairs, wearing tracksuit bottoms and no shoes or top.

He appears to be clean and calm – and at certain points he is walking with no hold on him.

At other points officers are using what is described as a “come along hold” – a light hold at his wrist.

The new footage runs until 07:29 when he enters the shower room.

There is then a gap because there are no cameras in the shower room.

Officers then go into the shower room at 07:48 and the restraint begins.

The footage shown previously shows Marshall being dragged out of the shower room, face down, by multiple officers and restrained by up to 17 officers, some of whom used their feet.

Marshall’s aunt Sharon MacFadyen, who has been campaigning on her nephew’s case for years, says the new footage “doesn’t fit” with what officers said at the time about him being agitated, aggressive and covered in excrement.

“If he was kicking off or if he was fighting fair enough, but he’s doing what he’s told,” she told BBC News.

She believes that Marshall, who had pressed his emergency buzzer several times during the night, had annoyed officers and was being taken to the shower room to be taught a lesson.

“There’s no cameras or anything. Since you don’t know what went on in there we’ve only got their word for it,” she says.

Sarah Armstrong, a professor of criminology at the University of Glasgow, said she was “shocked” to see how calm Marshall was in the footage.

“I don’t see anything in that video suggesting that use of force is required,” she says.

“There’s no sign that he was resisting.”

Prof Armstrong adds that there is no sign of any excrement and officers are not acting in any way that suggests a smell.

“It raises questions for me about the decision to take him into the shower, a room that had no cameras,” she says.

“There’s no physical sign that was required.

“That footage seems to contradict all of the reasons publicly given for, first of all, taking him into the showers and, second of all, exercising a restraint.”

All the prison officers involved in the restraint of Allan Marshall were granted lifetime immunity from prosecution to persuade them to give evidence at a fatal accident inquiry.

This was a decision the Crown Office later admitted was a mistake.

In an attempt to get what she sees as justice for her nephew, Sharon MacFadyen instead took a human rights case against the authorities involved in his death and the subsequent investigation.

It was the first in Scotland using article two of the Human Rights Act 1998 – breach of the right to life.

Police Scotland and the Crown Office agreed to pay compensation to the family last year but the prison service did not.

Judge Lady Ross is expected to make a decision next month on the levels of damages they should pay.

The Scottish Prison Service admitted in September that Marshall’s death was unlawful – 10 years on from the fatality.

Last September his family received an apology from the prison service, Crown Office and Police Scotland after the Court of Session heard that the level of force went beyond what was necessary.

It was the first time that all three parties publicly apologised, accepted it as an unlawful death and accepted that the state failed to adequately investigate.

A Scottish Prison Service spokesman said: “We sincerely apologise for failings which resulted in the sad death of Mr Marshall and our thoughts and condolences remain with his family.

“As proceedings remain live in this matter it would be inappropriate to comment further.”