Police have released CCTV images of a man being pursued by an armed attacker who eventually shot him in the neck.
The CCTV shows Charles Butler being chased and fired at
Charles Butler, 50, was attacked outside The Matapan pub in Dagenham, east London, on 13 October and remains in a coma on life-support.
The CCTV shows him being chased around a car and into the main road as the lone gunman fires at him repeatedly.
Officers have arrested three men, including a detective constable, in connection with the shooting.
But police are renewing their appeal on the BBC Crimewatch UK programme for more information about the shooting.
The CCTV shows Mr Butler stumbling in the street as he is shot by a man who then runs away, possibly to a red car in Stockdale Road.
Det Ch Insp Dave Brown said: "We appreciate that the CCTV footage being released is extremely graphic.
"But we are certain that someone will recognise the gunman and it is essential that he is apprehended as soon as possible."
Mr Brown also wants to trace the driver of a white car seen pulling into Mr Butler's drive an hour before the shooting.
Last month, a 47-year-old detective constable, based at the Specialist Crime Directorate was arrested at his home in Hornchurch, Essex, on suspicion of conspiracy to murder.
He has been suspended from his duties. A 41-year-old private investigator, from Borehamwood, Hertfordshire, was also arrested for conspiracy to murder and bailed.
Earlier last month, a 31-year-old man was arrested in connection with the inquiry and bailed.