Police baffled by student murder

Marsha had lots of friends and was doing a gap year

Detectives investigating the "vicious" killing of a student in south-west London have admitted a motive for the murder "remains a complete mystery".

Marsha McDonnell, 19, was clubbed three times over the head with a blunt instrument, possibly a hammer, just yards from her home in Priory Road, Hampton.

Police believe she was probably killed in a random attack by someone she had never met - either a mentally disturbed stranger, or a would-be sex attacker or robber.

Nothing was stolen and there was no evidence of a sexual assault.

Women have been warned to take extra caution

DCS Dave Cook

Detective Chief Superintendent Dave Cook said officers would contact east London colleagues investigating the death of Margaret Muller, who was stabbed to death while jogging in Victoria Park.

But he said there was "nothing to indicate a connection at the moment".

He said: "This person needs to be found, we need to be able to satisfy the public they are safe from this individual.

"This is a vicious, violent attack on a young girl in the early hours of the morning and the motive is a complete mystery.

"Women have been warned to take extra caution."

'Deliberate blows'

Ms McDonnell had been to watch the film Catch Me If You Can with friends and was on her way back to her parents' home when she was attacked from behind just after midnight on Tuesday.

"The motive is a complete mystery," DCS Cook said.

"We don't know what it was. It wasn't a frenzied attack. There were quite deliberate blows to the head."

Police say CCTV footage suggests Ms McDonnell was not followed

Forensic tests are being carried out to determine exactly what the weapon was.

DCS Cook said officers had already looked into the teenager's private life, and did not believe her murder was linked to that.

There was also no evidence that Marsha had been followed home after getting off a bus minutes before she was attacked, he said.

But he appealed for anyone who was at the 111 bus stop outside the John Lewis store in Kingston at about 2350 GMT Monday, or at the stop she got off in Priory Road at 0017 GMT Tuesday, to come forward.

Life support

Ms McDonnell was taken to hospital after being found injured but conscious on the pavement by a neighbour.

Ms McDonnell was found just yards from her home

She was surrounded by her parents and two sisters when her life support machine was turned off on Wednesday.

Police will continue to search the area over the weekend.

Ms McDonnell had been taking a year out after A-levels and was working in a shop while she saved up to go to Australia.

She was thought to have recently split up with her boyfriend but had been enjoying regular nights out with friends.

They described her as fun-loving, caring, and a brilliant violinist who was interested in photography.