THE husband of murdered rookie police officer Sharon Beshenivsky last night branded her killers "cowards".

Paul Beshenivsky said the armed raiders who gunned down his wife - and her colleague, Teresa Milburn - during a robbery in Bradford city centre, had taken away "a wonderful mum".

"The world is a darker place without her," he said.

Four men and a woman arrested on Saturday when police swooped on addresses in London, 200 miles from the scene of the murder, were taken to Yorkshire in an armed police convoy yesterday.

The convoy, with a police helicopter flying overhead, took the suspects to separate police stations in the West Yorkshire force area, where they are being quizzed by detectives.

A sixth suspect - a man - remains in custody in the capital.

PC Beshenivsky, 38, who had three children and two stepchildren, was killed on her youngest daughter's fourth birthday during a raid in a travel agents, in Morley Street, on Friday.

Mr Beshenivsky, a landscape gardener, said: "It breaks my heart to think I will never hear her infectious laugh again, to think she won't be here to see our children grow.

"When Sharon left for work on Friday, it was such a happy day.

"Our youngest daughter, Lydia, was celebrating her fourth birthday and she waited excitedly for her mum to come home.

"When Sharon was late, I knew something was wrong.

"The people who did this to Sharon and Teresa, and to our families, are cowards.

"They took away my wife, but they also took away a wonderful mum.

"She was my rock. She was loved by everyone who met her and my family's loss is felt by so many."

Mr Beshenivsky, who was allowed in to Morley Street within the police cordon to lay flowers at the scene, said his wife was proud to be in the police and he was proud of her.

The former childminder had been a community support officer for two years before joining the West Yorkshire force full-time nine months ago.

Although she was wearing body armour, she died after being shot in the chest.

PC Milburn, 37, who joined the force on April 5 last year, was discharged from Bradford Royal Infirmary shortly after 3pm yesterday.

She said last night: "Friday should have been another routine day at work - instead I lost a colleague and a dear friend.

"Sharon and I enjoyed working together immensely. Nothing can bring Sharon back, and my wholehearted sympathy goes out to her family."

The drama began at about 3pm on Friday when the three robbers, armed with guns and a knife, entered the travel agents. The men escaped with an undisclosed amount of cash.

The two female officers arrived in a squad car at 3.30pm, but two minutes later the control room received a Code Zero alert, indicating a police officer had been shot.

One of the gunmen opened fire as soon as the officers confronted the gang in the street.

Their injuries were treated by colleagues at the scene, one of whom had previously served in the armed forces as a medic. But PC Beshenivsky could not be saved.

PC Beshenivsky's mother, Jennifer Knee, visited the Morley Street scene yesterday with her partner.

They were allowed in the cordoned off area and looked at some of the many tributes on the flowers at the side of the road.

Meanwhile, the former head of the Metropolitan Police yesterday called for the death penalty to be reinstated for police killers.

Lord Stevens said the killer should lose his life, despite having always opposed capital punishment.

Writing in a Sunday newspaper, the former Scotland Yard commissioner said: "All my life I've been against the death penalty. But after the cold-blooded murder of policewoman Sharon Beshenivsky, I've changed my mind."

There were also calls last night to arm the police. But Home Office advisor Lord Mackenzie of Framwellgate said: "Having spent time with the FBI, I think arming the police would increase the problem. It would not have saved the situation in Bradford as the officers involved were shot almost as soon as they arrived at the scene."

Detective Sergeant Chris Pendlington, spokesman for the Police Federation with Cleveland Police, said: "I would say no to arming the police. My personal view is there are armed units on the road all the time. You can never account for what may waiting around the corner. But I would not like to see the police armed."

Jane Kenyon, chairwoman of North Yorkshire Police Authority, said: "I can understand why this debate has gained such momentum in the last 48 hours. It is a debate that the service and the communities need to have, but any knee-jerk reactions need to be taken very steadily."