Bradford prostitutes have been warned to keep off the streets or be more security conscious following the brutal murder of a teenage 'working girl'.

Police have stepped up patrols in areas used by prostitutes after Rebecca Hall's naked and battered body was dumped in an alleyway yards from where she worked.

And as detectives interviewed other prostitutes in a bid to trace the killer, they stressed clients were not the sole suspects.

Investigators believe Miss Hall - known as Becky to friends - was probably abducted and held captive for a number of days before dying from head wounds sustained during a savage and sustained beating.

The 19-year-old had not been seen since she left her Little Horton flat on Good Friday. Her body was found behind a car park in Thornton Street last Thursday.

Detective Chief Superinten-dent Max McLean said: "We are strongly considering the theory she was held captive because she did not have any contact with her baby boy in that time."

The infant - four-month-old Jordan - is being looked after by his grandparents.

Det Chief Supt McLean said a large number of officers were dedicated to catching the killer and a special incident room and hotline have been set up.

"Police patrols have been stepped up and we would urge prostitutes to be very cautious following this incident," he said.

"Prostitution places them in extremely dangerous situations and we would advise them not to go on to the street at all.

"But if they feel they have to, they should take precautions such as having a contact who knows where they are at all times."

He said there was no obvious sexual motive and no evidence of abuse in the time Miss Hall was missing.

"We are not only looking at clients as possible suspects and are keeping an open mind on the issue," he added.

Someone who knew Miss Hall outside of prostitution may have murdered her, he said.

Det Chief Supt McLean said there were no strong links to any previous attacks on 'working girls' but added that officers were reviewing past cases: "Officers have been actively going out to speak to working prostitutes and they have contacted us with information and reports of assaults upon them which we will investigate."

He said they would often not report such attacks to police, but in the light of the murder had been doing so. Anyone with information, or who knew Miss Hall, should contact the free-phone number 0800 818001.