AN ARMED gunman forced an employee of a Dublin headshop and two customers into the backroom of the store before he and an accomplice set the place alight in an arson attack that has now been upgraded to a triple attempted murder investigation.

The captives were forced to run through flames to escape from the Happy Hippy Store, on North Frederick Street, after the criminals fled the scene on Tuesday night.

A senior source said that the three people could "very easily have been burnt alive". CCTV has revealed that one of the two criminals, whose faces were covered with hoods, almost set himself alight after he doused the place in petrol.

It has also emerged that the totally innocent shop employee is related by marriage to members of a well-established criminal gang based in Dublin city.

The gang are major distributors of cannabis in Dublin and detectives are probing whether the young man was targeted because of his family background and whether his relatives will now retaliate.

"It's frightening. The three of them could have easily been burnt alive. If they panicked, they were goners. But luckily, they ran out of the shop quickly and got through the flames okay," said a source.

"They were forced into a room off the back of the shop. There was no back door out. The two men weren't looking for money. This was undoubtedly attempted murder."

One of the two criminals was armed with a handgun. The other had a small container of petrol. When the three people were forced into the backroom, the latter liberally doused the place in petrol and set it alight.

Moments later, the two customers and the shop employee rushed through the flames to get out the front door after a loud explosion.

Detectives at Fitzgibbon Street are leading the investigation into what another senior detective described as "one of the most horrific and unprovoked attacks I've ever seen".

Senior gardaí have not yet identified the two criminals but the seriousness of the incident has resulted in considerable garda resources being allocated to the case.

One main line of inquiry is that those responsible are members of a drug-dealing gang that are targeting headshops because the legal highs sold there are eating into sales of cocaine and ecstasy.

It is also understood that some local people living in the vicinity of North Frederick Street are unhappy with the proliferation of headshops in the area and supported the criminals in their arson attack, though not the attempted killings.

The attack took place just after 9pm on Tuesday. The fire brigade managed to control the fire, which did not destroy the store.

The incident came just five days after the Nirvana head shop on Capel Street and two businesses beside it were completely gutted when a fire took hold inside the head shop.

A focus of the garda investigation is to establish whether the two attacks were part of an orchestrated campaign.

The owner of the Nirvana store, Jim Bellamy, said the fire had been started intentionally and he feared for his other businesses.