A £50,000 reward for details leading to the arrest and conviction of the killers of a police officer in Bradford is being offered by Crimestoppers.
Pc Sharon Beshenivsky was shot dead and her colleague wounded
Pc Sharon Beshenivsky died at the scene and her colleague PC Teresa Milburn was seriously injured in the shooting on Morley Street on 18 November.
Yusuf Jama, 19, is being held by West Yorkshire Police over Pc Beshenivsky's murder outside a travel agents.
Magistrates granted police a further 36 hours to question Mr Jama on Monday.
He was arrested on Saturday after police were called to a house in Saltley, Birmingham, over an allegation of serious sexual assault.
Yusuf Jama was arrested in Birmingham
Two other men - Muzzaker Imtiaz Shah, 24, and Mr Jama's brother Mustaf, aged 25 - who are wanted in connection with the crime are still at large.
Pc Beshenivsky and Pc Milburn were shot after an attack alarm had been set off and they were sent to investigate at the Bradford travel agency.
Det Supt Andy Brennan, from West Yorkshire Police's Homicide and Major Inquiry Team, said he believed there were people who knew the whereabouts of those who had committed the crime.
He said: "The investigation team welcomes the use of the reward offered by Crimestoppers.
"We are continuing to receive a lot of support from the general public. This was an horrific crime.
"It may be that you have some information which will help us but, for whatever reason, you are unsure about coming forward."
He reassured the public that all calls to Crimestoppers are anonymous.
" If your information leads to the conviction of the people responsible for this crime, then you could claim this reward," Det Supt Brennan added.
Five Somali men and a woman, arrested in London in the aftermath of the shooting, have been released.
The men were all bailed pending further inquiries and the woman was freed without charge.
On Tuesday colleagues of Pc Beshenivsky thanked the people of Bradford for their support.