Rewards totalling £25,000 have been offered to help catch the gunman who shot dead a police officer and left another seriously injured.
Ian Broadhurst leaves a wife, Eilisa
Pc Ian Broadhurst, 34, died in the shooting in Leeds on Boxing Day and his colleague Pc Neil Roper, 45, was injured and is recovering in hospital.
A third beat officer, who went to his colleagues' assistance, may also have been shot at during the attack.
The shooting happened after Pcs Broadhurst and Roper stopped a stolen BMW car in Dib Lane in the Oakwood area of the city.
After they tried to arrest the driver, he pulled a gun and began shooting.
He escaped in a green Rover 600 car which was found abandoned in nearby Springwood Road just after midnight.
Neil Roper's family are at his bedside as he recovers in hospital
The News of the World and film producer Michael Winner have announced a joint £20,000 reward for help in catching the killer.
The newspaper's managing editor Stuart Kuttner said: "Police risk their lives for the rest of us every day. We want to give the West Yorks officers every support we can."
And Norman Brennan, director of Protect the Protectors, said a £5,000 reward was being put up by the police campaign group for information leading to the arrest and conviction of the killer.
He said: "Armed criminals have complete disrespect and my colleague has paid the ultimate price for trying to make society a safer place.
"This indiscriminate murder yet again begs the question, when do we fully arm the British police
Detective Superintendent Chris Gregg, who is leading the inquiry, appealed for witnesses to come forward.
Eilisa Broadhurst is said to be devastated at the loss of her husband
"We are appealing for any information that can help us track down this man, who can only be considered as exceptionally dangerous.
"This was an appalling, dreadful, callous attack on unarmed officers."
Pc Broadhurst, who was born in Sheffield, had joined the road traffic police only last March, fulfilling a long-held ambition for the car enthusiast, West Yorkshire's Chief Constable Colin Cramphorn told a news conference.
His wife Eilisa, from Glasgow, was said to be in a state of
disbelief and extreme shock over what had happened.
The couple, who lived in Cookridge, Leeds, and had no children, married two
years ago after meeting on holiday in Tenerife.
all a very close family," said Mr Cramphorn.
Pc Roper, of Wakefield, is a married man with two children, aged 10 and seven. His family are at his bedside in hospital.
The third officer involved, who is in his 20s, was close to the vehicle when the gunman opened fire and his radio harness was damaged, possibly by a bullet.
Mr Cramphorn said: "This has been a devastating blow to West Yorkshire Police.
High profile police deaths
1984 - Pc Yvonne Fletcher shot dead outside Libyan Embassy
1985 - Pc Keith Blakelock killed in Broadwater Farm riots
1992 - Special Constable Glen Goodman killed by IRA near Tadcaster
1993 - Pc Patrick Dunne shot dead investigating a shooting in Clapham, London
1995 - Trainee Pc Philip Walters shot investigating a domestic incident in Ilford, east London
1997 - Pc Nina Mackay knifed by paranoid schizophrenic in
2000 - Pc John Odell hit by a car in Margate, Kent
2003 - Det Con Stephen Oake stabbed to death in Special Branch raid in Manchester
"It has been 19 years since an officer was murdered on duty in this way in West Yorkshire.
"When circumstances like this strike any police service it is the time you realise we are actually an extended family.
"And like any family that suffers a massive shock people gather round and you see the best of those individuals."
The gunman responsible for the death of Pc Broadhurst should face the death penalty, the former chief constable of the force said later.
Keith Hellawell called for a change in the law so that people would be hanged for shooting a police officer.
He told BBC Radio 4: "We ought to make it clear to people that if you shoot a police officer you are going to be hanged if convicted."
The shooting took place as the stolen car was being transferred to a towing truck, and the driver was being questioned in the police car.
Pc Roper, whose injuries are not thought to be life-threatening, gave a description of the gunman: a white man, of stocky build, in his 30s or 40s and with a tanned or olive complexion.
The gunman ran off down Dib Lane, past a row of shops, shooting indiscriminately as he went.
He threatened a passer-by, who police would also like to trace, before forcing the owners of the Rover car to hand over the keys so he could make his getaway.