It was one of the most gruesome murders Wandsworth had ever seen. Now it has become the most intriguing.

Who knocked on Andrew Cunningham’s caravan door one cold December night last year?

Who was angry enough to stab him to death – and, even more horrifying, mutilate his genitals?

Today is the first anniversary of the 52-year-old sex offender’s death in Riverside Road, Windmill Business Centre in Earlsfield.

Rumours have spread to every cranny of the borough, although in reality, very few people claim to know what happened for sure.

More than 350 witness statements have been taken, but police still have no concrete leads.

This week officers visited the scene in the hope that those covering up for Cunningham’s killer may have changed their allegiances since last year. After all, it is not the richest of areas and a reward of £20,000 will go to whoever can help convict them.

Detective Inspector Alison Hepworth said: “This is a vicious killing. Someone must have a clue who has done it.

“We are still reviewing CCTV. There’s not any witnesses coming forward that we can speak to. We are emphasising the reward and visiting pubs in the area, trying to keep it in people’s minds.”

It was some time after 6.10pm on Tuesday, December 9, last year, that Mr Cunningham heard a knock on the door of his caravan. Police believe he may have known his killers, because there was no sign of a struggle or forced entry.

Whoever it was ransacked the place – opening Christmas presents and stealing a wallet containing up to £6,000. They also took a distinctive Scottish £100 note, although this has never been traced.

When police found him the following day at 8am, he was dead in a pool of blood – with stab wounds to the head, neck, chest and groin.

Since then, three people have been arrested but were bailed, with no further action taken.

A mysterious laugh was played on Crimewatch but it turned out to belong to an innocent man. The investigation seems cursed by red herrings.

DI Hepworth said there was a “strong possibility” the team had already spoken to the killer. She said there must be people who saw them afterwards, with blood-stained clothing, who are covering for them.

According to Jennifer Brown, professor of forensic psychology at the University of Surrey, statistics show killers of this sort are more likely to be a stranger to the victim but familiar to the location of where the body was found.

She said: “Statistically, mutilation especially to genitals of murder victims is relatively unusual. It is probable that the murderer or murderers have previous convictions themselves, possibly a violent offence. It is more likely to be a male offender and white.”

Locally, three plausible theories have emerged over the past year.

The first is that his killer was a vigilante who knew Mr Cunningham had been convicted of sex with a 15-year-old girl in 2001.

Locals also said there were rumours of him interfering with a local two-year-old, although police said there was no evidence of this.

A rumour circulating in the pubs of the area said four men set out to teach him “a lesson” – but went too far. One of those men was said to be mentally unbalanced, and perhaps acted as the ringleader.

But police have always dismissed this theory, saying it was most likely a burglary that turned nasty, because of the theft.

A similar theory was put forward by a family friend of Mr Cunningham, Lucy, then 14, who said he was in arguments with several people who owed him money.

DI Hepworth said: “You do get rumours coming out. But none of them are leads. We would say they’re rumours and speculation. Nothing’s come in that is concrete.”

The community, which centres around the Corner Pin pub, are a closed-off group who are suspicious of outsiders poking into what they see as their business.

Whether through loyalty to the killer or fear, police believe some people may have avoided speaking about the incident.

But DI Hepworth stressed the importance of finding such a violent killer, who could still be at large in the area.

She said: “I would think if someone’s killed like that, there’s a strong possibility they will kill again. If people are that way inclined it’s a difficult behaviour to stop.

“These investigations aren’t just down to the police. The public have to help to solve these crimes.

“And if we don’t have the help from the public it becomes more problematic to find out who’s killed him.”

If you have any information about this crime, call the police incident room on 020 8721 4005 or to remain anonymous call Crimestoppers on 0800 555 111.

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