Anyone who saw the Toyota Rav 4 last Friday is urged to contact police
A man quizzed in connection with the murder of Pc Sharon Beshenivsky says police should have followed up his concerns about a gang in London.
Shahid Khan, from west London, claims he was forced to hire the car believed to have been used by the gunmen.
Detectives are still hunting three people over the shooting of the 38-year-old and her colleague, Teresa Milburn, 37, in Bradford, West Yorks.
Police say no formal complaint was made by Mr Khan, who has been freed on bail.
Mr Khan, 31, says he went to police after the gang forced him to hire a silver Toyota car which police believe was used by the killers.
He said: "I went to the police station and reported it and the policeman - I don't know if he didn't take me seriously or something, because I was telling him: 'Why don't you check it.'"
Mr Khan was arrested by armed police on Saturday and driven to West Yorkshire, where he was interviewed for three days.
He was freed on bail after telling detectives Somalian drug dealers had blackmailed him to hire five cars for them after he unwittingly rented a room to one gang member.
Mr Khan said that although the lodger seemed friendly at first, he soon started to bring back friends and used the home to deal drugs.
But he insisted that after he remonstrated with the man about his activities, he was threatened and even kidnapped.