Gardai are hunting three men seen running from a car they believe may have been used in Dublin's latest gangland style murder.
The victim was gunned down in a housing estate near his home in Greenfort, Clondalkin, in the west of the city, early today.
A senior garda source said he had received "multiple gunshot wounds" to the head and body, and that investigating detectives would "keep an open mind" as to a potential motive for his murder.
The incident happened at around 12.20am at Harelawn Green, close to The Finches pub.
Gardai responded to reports of gunshots and found the victim slumped over with serious injuries.
He was taken to Tallaght Hospital where he was pronounced dead.
A burning car was discovered a short time later at Collinstown Crescent, just over one kilometre from the murder scene.
Gardai believe the vehicle - a black Vauxhall Vectra with tinted windows and registration 99 DL 7997 - may have been used as a getaway.
They preserved the car for a forensic examination and appealed for anyone who may have seen it to come forward.
The scene of the shooting was also sealed off for technical investigations to be carried out.
As a post-mortem examination on the body by Deputy State Pathologist Dr Michael Curtis got underway, there was widespread condemnation throughout the working-class area.
Sinn Fein councillor Matthew McDonagh said Clondalkin had seen too many gangland-style shootings over the years.
"These young victims, regardless of what they're involved in, are just taken off the face of the earth, and for what?" Mr McDonagh said.
"So many families have lost people close to them and this incident is no different. Another family has been left devastated."
The councillor has lived in the area since 1977 and knows the victim's father.
"I have seen a lot of changes over the years," he said.
"Greenfort, next to Liffey Valley where the lad was from, is just like every other working class area. It's had its ups and its downs. But this is something you can never prepare for."
Local sources said they believe Mr Johnston was shot between eight and 14 times.
Fianna Fail councillor Trevor Gilligan urged locals to stick together during the difficult time.
He said, despite its history of similar shootings and murders, Clondalkin remained a strong area with "great community spirit".
"I strongly condemn any shootings or any acts of violence and I would urge the community to stick together," Mr Gilligan said.
"Regardless of the circumstances surrounding this murder, we have to remember that someone has lost a son, and our sympathy and commiserations has to be with his family and friends."
A Dean Johnston was murdered in May 2011 as he sat in the back of a car outside the home of his best friend on Moorefield Avenue, Neilstown.
The 20-year-old was killed when a man walked up to his friend's VW Golf car and fired five shots from a handgun into a rear passenger window.
He was hit in the head and shoulder and was later pronounced dead at Tallaght Hospital.
Mr Johnston lived a few doors away from where the shooting happened - at the other end of north Clondalkin where his near-namesake was gunned down today.