Three years after his 15-year-old son was gunned down at his front door, a grieving father again appealed to the Clapham community to name his murderer, as he described the daily torment of knowing his son’s killer walks free.

Billy Cox, who died on Valentine's Day 2007, was held by his 13-year-old sister Elizabeth as he bled to death from a gunshot wound to the chest, in what police believe was a drug-related incident.

Despite detectives being “confident” they know the killer, and “several” people naming the same man, evidence - even with the promise of a £20,000 reward - has not been strong enough for a conviction.

Standing next to his son’s mural in the Fenwick Estate, Tommy Cox said he still can’t speak to his daughter about the tragic events of that day.

Mr Cox, 55, said his family’s feeling of loss and anger were as raw as three years ago, and while catching the killer would help, it would never repair the damage to his family.

“Being here three years on doesn’t help, it doesn’t change things," said Mr Cox, a builder.

"It has been three years but nothing has changed. We all miss Billy and nothing is going to bring him back.

“The individual that did it is still walking the street. Police won’t tell me who it is but I want to have a chat with them and ask them why they did it.

“Everyone around here knows who did it, even the individual’s mother. I don’t know how she can look in the mirror. She needs to do the right thing.

“After three years maybe people who know the killer can come forward. If they knew the hurt and pain caused to my family.”

He said while the events devastated him and his wife, they still speak to their son, but the bloody event will forever scar their daughter in a different way.

“It has put our marriage under strain but we are still strong together,” he said. “But it has been very hard on my daughter.

“She was 13 at the time. We are close, but to this day we cannot speak about what she saw that day.

“We can talk about Billy and what he was like and she has photos of him all over her room. But we can’t speak about that.”

Anyone with information should contact the incident room on 020 8247 4553 or Crimestoppers anonymously on 0800 555 111.

Police investigation

The detective leading the investigation into Billy Cox’s murder has said people who witnessed the murder know the killer - and one piece of information could bring the murderer to justice.

Detective Inspector Russell Duke, of the Metropolitan Police’s Trident team, said despite “several” pieces of information naming the same man, the evidence needed to be stronger to secure a conviction.

He said after three years he hoped people had now realised they had a responsibility to help catch the killer and “just one person coming forward could be enough”.

He said: “Maybe you saw the killer, maybe they gave you a gun after the killing, or you saw them in an agitated state?

“Just one piece of evidence could be the key to catching them. The gun used was a self-loading pistol, which we haven’t found. If anyone knows where that is that would help.”

He said as allegegiances change and people get older they “become aware of the right thing to do”.

He said: “We want to speak to anyone who phoned us at the time of the murder or anyone who has anything new to add.

“We are very good at helping people who give evidence. We have done it countless times before and new evidence from people who saw what happened is crucial to get a conviction. We need someone we have spoken to previously.

“Were you in or around Fenwick Place that afternoon, Billy's home backs on to Cottage Grove? Did you see or hear anyone, either in front or at the rear of the property between 2.30pm and 3.30pm?

"After three years, we believe that anyone who knows who killed Billy Cox should feel that they can tell police what they know. We will treat all calls in the utmost confidence and urge you to pick up the phone, for the sake of Billy's family."

What happened that day?

On February 14, 2007, Billy returned home Cottage Grove, Fenwick Place. About 3.30pm he answered his front door and was shot.

Police said there were no signs of forced entry and Billy may have known his killer. His sister, then aged 13, was returning home from work and heard a 'bang' as she got near the home and once inside she found her brother dying.

The backdoor of the house was open and investigators believe the gunman escaped on foot down Cottage Grove carrying a nine millimetre handgun.

A friend helped her to give first aid while they waited for an ambulance and a paramedic also treated Billy, but he was pronounced dead at the scene.

A post mortem examination gave cause of death as a gunshot wound to the chest.

timeline

•Feb 14, 2007 - Billy Cox killed at his Cottage Grove home about 3.30pm.

•June 6, 2007 - Officers arrest five men at an address near Clapham High Street. Four arrested on suspicion of possession of Class A drugs with intent to supply and were later released without charge.

A fifth man, then aged 20, was arrested on suspicion of the murder of Billy Cox. He was later released without charge.

•Feb 14, 2008 - Police offer a £20,000 reward for arrest and conviction of murder to mark first anniversary of Billy’s death.

•Oct 31, 2008 - Inquest into Billy’s death returns a verdict of unlawful killing.

• Feb 14 2010 -Police launch third anniversary appeal to catch killer.