Republican paramilitaries from the Irish National Liberation Army (INLA) were behind the murder of a west Belfast man outside a school last year, police believe.
Jim Donegan, 43, was gunned down in a hail of bullets in December as he sat in his car waiting to collect his teenage son.
Detectives said the same killer had been waiting for his victim at the scene five days earlier but Mr Donegan did not pick up his 13-year-old that day.
They blamed the INLA for the killing.
Detective Chief Inspector Pete Montgomery said: “Today I am releasing new CCTV footage which I believe shows the gunman, five days before Jim’s death, waiting for him to arrive to collect his 13-year-old son with hundreds of innocent children nearby.
“Jim was not collecting his son that day but I believe that, if he had appeared, he would have been murdered at this point.
“My investigation into the callous execution of Jim Donegan continues to progress and a republican element is a main line of inquiry, specifically the INLA, but I really need the public’s help to remove this dangerous man from our streets.”
The INLA was a small but active republican paramilitary grouping during the Troubles.
It killed Margaret Thatcher’s Northern Ireland spokesman, Airey Neave, in 1979 and leading loyalist Billy Wright in 1997.
It was behind one of Northern Ireland’s bloodiest atrocities when it killed 17 people in a bombing at the Droppin’ Well pub in Ballykelly, County Londonderry.
The armed group said it had decommissioned weapons almost a decade ago but independent monitors have said it remains deeply involved in serious crime.
Mr Montgomery said the suspect in Mr Donegan’s shooting may be in his late 30s to early 40s, approximately 5ft 8in, and may walk with a limp or may have an existing medical condition which affects his gait.
He added: “This is someone who thought it was acceptable to put the lives of countless children at risk and murder Jim – please help me put him before the courts.”
On the day of the murder, Tuesday December 4, police said the gunman emerged from Clonelly Avenue on to Glen Road in Belfast at around 3.10pm.
He then walked past numerous children at around 3.15pm, “calmly” activated the pedestrian crossing, crossed the road and walked up the victim’s car, firing his weapon eight times before fleeing the scene, police said.
He was wearing a high-visibility hip-length yellow jacket with “Security” written on the back, dark trousers, and a grey-coloured hat or hood. He was carrying a dark bag over his shoulder which detectives believe contained the gun.
Investigators have appealed for anyone in the area at the time to tell them what they saw or give them any footage.
Mr Montgomery added: “The family have been left devastated and hundreds of children and families who witnessed the murder have also been left traumatised.
“The callous actions of the gunman will have catastrophic psychological effects on them all.”