DETECTIVES investigating the murder of prison officer David Black revisited the scene of the killing today to appeal for information.
Mr Black, a 52-year-old father of two, was gunned down in a high-speed motorway ambush as he drove to work at Maghaberry prison in Co Antrim exactly a week ago.
PSNI Assistant Chief Constable Drew Harris said the detectives hoped to jog drivers' memories.
He said: "We are doing this because we believe it may be of assistance in catching David Black's killers. We apologise for any delays or disruption but this is a murder investigation."
A 40mph speed limit was imposed on the stretch of the M1 between Portadown and Lurgan, where Mr Black's black Audi was forced off the road when shots were fired from a dark blue Toyota Camry at about 7.30am last Thursday.
Checkpoints were mounted at a number of locations close to the M1 where police officers spoke to motorists and handed out leaflets appealing for information.
Vehicles in the Annesborough Road area of Lurgan were also stopped as part of PSNI enquiries to determine whether it was used as a getaway route by Mr Black's killers.
Dissident republicans have been blamed for the shooting.
Mr Harris described the murder hunt as a substantial and complex investigation.
He said: "We have a large amount of CCTV material to analyse in relation to Mr Black's Audi, registration number HHZ 1560, and the killers' Toyota Camry, which had a southern registration number 94 D 50997.
"We really do need to hear from anyone who has any knowledge about the Camry car in the days leading up to the murder or who saw it on Thursday morning.
"We also need to speak to anyone who was on the motorway travelling eastbound towards Belfast last Thursday morning, whether they joined it at Tamnamore, Loughgall, the Birches or Portadown."
A spokeswoman for the PSNI said a man arrested in connection with the murder earlier this week was still in police custody.
Three others including prominent Lurgan republican Colin Duffy and a 29-year-old man detained in the Republic were released without charge.
The Crimestoppers charity has offered a £10,000 reward for information that leads to the conviction of Mr Black's killers.
At his funeral yesterday Mr Black's daughter Kyra described the prison officer as her special hero.