Detectives are hunting four men over a cowardly attack on a homeless drug addict.

Matthew Heading, 41, who was staying at the Glenwood Lodge Hotel in Grand Parade, Brighton, was found dead in his room last Friday.

Two days earlier, he had been assaulted while sitting on some steps with a friend in Grand Parade, Brighton.

Detective Chief Inspector Graham Pratt, leading the investigation, said: "It was a violent and cowardly attack on a clearly vulnerable man.

"I can't imagine why they did it.

"There's no reason to suggest he knew his attackers. We've no idea what may have been said or done to provoke the assault and won't until we've spoken to those involved."

It is thought four young men were involved. Post mortem tests showed Mr Heading had severe internal abdominal injuries consistent with the assault on him.

Mr Pratt said: "I'm quite satisfied they were caused as a result of a kick or a punch."

No arrests have been made and police are attempting to enhance CCTV footage of the attack.

Mr Heading was taken to the Royal Sussex County Hospital, Brighton, where he spent five hours being treated for minor injuries.

But his internal injuries were not discovered.

He left the hospital and appears to have been fine on Wednesday and Thursday nights but did not wake up on Friday morning.

Mr Heading's companion was injured and cannot remember full details of the attack.

Mr Pratt said: "It was a busy time of day on a main thoroughfare in Brighton.

"The assault spilled on to the road, so cars would have had to drive around Matthew.

"Maybe they didn't realise the significance of what they were looking at but he has died as a result and we need to speak to as many people as possible about it."

Sussex Police knew Mr Heading through their street intervention team which clears addicts from public areas.

His brother Simon, 38, from Peacehaven, said he had not had a proper conversation with Matthew for about three years.

He said: "Obviously I have the impact of losing a brother and it's bad.

"He was a very heavy drug addict and this is why he was at this hostel, because his body was falling apart.

"The drugs had really got to him.

"I think it was random. Obviously he was involved in drugs but nothing was stolen from him and he had money in his pockets.

"It's come at a very bad time. We have just sold our house and my mother and I are moving away in a camper van."

Sussex Police are looking for a group of four young white men in their teens and early twenties.

One was about 5ft 10in, wearing jeans and a white baseball cap, a second who wore a dark tracksuit and a blue baseball cap, and a third man who had three-quarter length jeans, a dark coloured top and a Mohican haircut that was growing out.

Police also want to hear from potential witnesses including a man in his late 30s who was holding a Cash Converters bag and a younger woman who was with a child in a pink-coloured buggy.

Anyone with information should contact Sussex Police on 0845 60 70 999.