A former youth worker wrongly arrested for murder after battling to save a man’s life is finally starting to get his own life back on track more than four years later.

Nathan O’Brien, from Greenhithe, was just 19 when he discovered Marcus Innocent bleeding to death on the pavement after being shot twice at close range by a gang member in a tragic case of mistaken identity.

Mr O’Brien’s first aid training kicked in and he performed CPR while telling his friends to dial 999, shooing young children away from the horrific scene and even trying to stem the bleeding from the two gunshot wounds in Mr Innocent’s stomach.

Even though Mr Innocent died, Mr O’Brien was praised by police and paramedics at the scene for his efforts.

But things took a turn when a senior police officer asked Mr O’Brien and his two friends, Jermel Taylor Crawford and Cieran O’Kane, to accompany him to the station.

Now a father of two, and aged 23, Mr O’Brien said: “We were driving through Woolwich on November 19, 2012, when I saw a group of young kids, probably aged about 10 and 11, standing around a pair of legs. I pulled over to see if I could help.

“I recognised Marcus. He used to sell CDs and everyone knew him. It wasn’t a pretty sight. What those kids saw is probably still affecting them today.

“I actually felt quite calm. I had my friends around me for support and I knew it was one of those situations where you can’t panic.

“If there was going to be any chance of him surviving I had to do something straight away.

“I started doing CPR while talking to the ambulance person on the phone but I could hear a horrible noise every time I pushed down on his chest.

“The person on the phone said I needed to lift up his top and put something over the gun shot wounds.

“That was the worst thing I could have done. I can still see the sight now.”

He said he performed CPR for 10 minutes until two police officers arrived, then for another five minutes until an ambulance pulled up.

Mr O’Brien, who is now father to a five-year-old boy and two-year-old girl, and lives in Russett Walk, watched as paramedics took over and tried to save Mr Innocent but he died at the roadside.

He said: “When the doctor said he was dead I went and sat in my car in shock. I think that’s when it hit me.”

As the three friends sat in Mr O’Brien’s car, trying to process what had happened, a senior police officer approached and asked the trio to accompany him to the police station to give statements.

Mr O’Brien continued: “I told him I was happy to give a witness statement at the scene but I hadn’t seen what happened and had only stopped to give first aid. He said it was ‘not an option’ to give a statement at the scene.”

After their refusal to go to a police station, all three were arrested on suspicion of murder.

Mr O’Brien said they were taken to separate police stations and he was held for about 40 hours, still with blood on his hands and clothes from trying to save Mr Innocent.

Officers took nail clippings and swabs from their hair and ears and their bail conditions prevented them contacting one another. Several months into the investigation, the allegations against all three were dropped but the damage had been done.

Mr O’Brien said: “Until recently I suffered with post traumatic stress disorder.

“When I used to eat certain foods the texture would bring back horrible flashbacks.

“I had nightmares about being put away, and hearing sirens or seeing police was horrible.

“I haven’t gone back to work yet. It’s still affecting me now but not as much.

“I still have problems eating certain foods and I don’t like being in crowded places.

“But sometime towards the middle of this year I’m hoping to open my own business. Just something basic, like hiring skips and things.”

More than four years after the ordeal started, Mr O’Brien received a written apology from the Met Police and an out of court settlement of £15,000, which he said he accepted because he wanted to put the incident behind him.

Mr O’Kane, 23, and Mr Crawford, 26, received £12,500 and £10,000 respectively.

A letter to Mr O’Brien from Debbie Ralph, head of misconduct and hearings in the Met Police’s directorate of professional standards, said: “I have no hesitation in acknowledging that you had no involvement whatsoever in Mr Innocent’s murder.

“Moreover, the MPS is grateful to you for taking it upon yourself to try and save Mr Innocent’s life by commencing CPR and continuing to assist with first aid after police had arrived on the scene.

"I had nightmares about being put away, and hearing sirens or seeing police was horrible" - Nathan O'Brien

“Police officers, dealing with horrific incidents such as this, often have to make dynamic and difficult decisions as to whether certain persons might have been involved in the offence and should therefore be arrested.

“In this instance a decision was made, in good faith, to arrest you. However, in all the circumstances, arguably you should not have been arrested, and for that, on behalf of the MPS, I apologise.”

After the apology, a Met spokesman said: “The Metropolitan Police settled a civil claim brought by three men for false arrest following the murder of a 35-year-old.

“A settlement was reached for an undisclosed sum and they received an apology.”

Mr O’Brien already had a criminal record of five public order offences and one criminal damage conviction, but says he had begun to turn his life around at the time of the shooting and was teaching mechanics to troubled youngsters at a youth motor project in Deptford.

A few months earlier he had been charged with witness intimidation but charges were later dropped when police realised it was a case of mistaken identity.

Former soldier Daniel Burgess, of Weardale Avenue, Dartford, was found guilty of murder at the Old Bailey and ordered to serve a minimum of 28 years before being considered for parole.

Perry Sutton, of Downs Farm, Green Street Green Road, Dartford, was locked up for 10 years after he was found guilty of conspiracy to commit GBH.

Jack Brennan, Patrick Brennan, Richard Brennan and Sonny Murphy, all from London, were all jailed for their part in Mr Innocent’s death but police believe up to 20 gang members travelled from Kidbrooke to Woolwich that day before the attack.

DC Toby Carroll, of the Metropolitan Police, said of the murder: “Marcus Innocent was not involved in gangs.

“However, he was wrongly set upon by what we believe was a 20-strong gang over a feud they had with another man, about a broken car window.”