A 36-year-old police officer has died and another man is in a serious condition after a triple stabbing.
Pc Jonathan Charles Henry was responding to an attack on a window cleaner in George Street, Luton.
The police officer died at Luton and Dunstable Hospital where two other victims are being treated.
Officers used a baton round and Taser electric stun gun to restrain the knifeman. A man has been arrested on suspicion of murder.
One of the injured men, a 55-year-old Luton man, was said to be in a serious but stable condition.
Police have not given details of the second man but said he was also being treated in hospital.
Colleagues have been left "traumatised" by the killing of Pc Henry, who was wearing a stab proof vest, said Chief Constable Gillian Parker of Bedfordshire Police
She said: "Jon loved his job and was a dedicated member of the police force.
"His dedication to duty cost him his life."
He leaves a wife Mary and a baby girl called Maggie.
At a press conference at Luton police station, Det Supt Keith Garwood refused to reveal the exact circumstances surrounding the officer's death.
He said Pc Henry was attending 999 calls from two members of the public after a man, said by witnesses to be a window cleaner, was stabbed in the back.
He attended in a marked police car and was with a number of other officers when he was attacked.
Home Secretary John Reid said he was "deeply saddened" by the death.
He added: "Such events highlight the dangers that police officers face every day on the front line protecting the public.
"This is a tragic event and I offer my deepest sympathy to the officer's family, friends and colleagues."