PSNI detectives investigating the murder of prison officer David Black have returned to a number of key locations close to the scene in a bid to get fresh information about the shooting.
Mr Black, 52, died after his car was ambushed on the M1 in Co Armagh last Thursday.
He was on his way to work at Maghaberry Prison when the attack was carried out.
Mr Black, from Cookstown, Co Tyrone, had worked for over 30 years in the prison service and was nearing retirement.
Electronic signs with a message appealing to motorists for information have been erected on the M1 eastbound between junction 11 at Portadown and junction 10 at Lurgan.
Officers earlier imposed a 40m/h (64km/h) speed limit on the stretch of motorway between the two junctions where Mr Black's Audi was approached by a dark blue Toyota Camry and a number of shots fired.
Police also mounted checkpoints at a number of locations and motorists were stopped, spoken to and given leaflets appealing for information.
Assistant Chief Constable for Crime Operations Drew Harris said: "The investigation into David Black's murder is substantial and it is complex.
“We are working closely with colleagues in a number of partner agencies, most notably An Garda Siochana, to follow various lines of enquiry.
"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."
He appealed to anyone with information on the Camry in the days leading up to the murder or anyone who saw it on 1 November to contact the PSNI.