At 12.20am and 20 seconds in Utah today Ronnie Lee Gardner became the first American in 14 years to be put to death by firing squad, his heart ripped to pieces by bullets blasted from the rifles of five expert marksmen hidden behind a brick wall.

The state attorney, Mark Shurtleff, tweeted the news. "I just gave the go ahead to Corrections Director to proceed with Gardner's execution," he wrote, adding: "May God grant him the mercy he denied his victims."

Then, with relatives of the condemned man's victims looking on behind bullet-proof glass, he became only the third person to die by firing squad in the US since 1977.

All three took place in this western state, which has long prided itself on its passionate embrace of the gun.

Utah is the only state in the US other than Oklahoma that lists the firing squad as a possible means of execution, offering condemned men the choice between that and the lethal injection.

In April, Gardner chose to die by the gun, telling a judge: "I would like the firing squad, please."

The manner of the execution shocked many across America, with critics claiming it was a throwback to the brutal blood-begets-blood mentality of the frontier era. Demonstrations were held on the steps of the Utah State Capitol building in central Salt Lake City and a prayer vigil was held at the Catholic cathedral.

Gardner ate his last meal of steak, lobster tail, apple pie, vanilla ice cream and 7UP soda on Tuesday, choosing to fast until his death.

The prisoner's extended family of about 20 brothers, sisters, daughters and grandchildren were assembled outside the prison, having strung up dozens of coloured balloons, which they released as soon as news came through of Gardner's death, as a symbol of his soul going up to heaven.

His daughter Brandie told the Guardian that Gardner explained to her why he opted for the firing squad. "He told me: 'I lived by the gun, I murdered with a gun, so I will die by the gun'."

Brandie, 33, said she was strongly opposed to the death penalty, even though Gardner approved of it. "I oppose it not because of my dad but because there are 10 commandments and one says thou shalt not kill."

The family of one of the victims – Nick Kirk, who was shot in the stomach as Gardner tried to escape from a courthouse and died 10 years later – were also outside the prison, demonstrating their support for his execution. "You don't want to wish somebody dead," said Kirk's daughter Barb Webb. "But our family wants this finished – we need to heal."

Kirk's wife, BelDean, and granddaughter Jamie were among 25 people who watched the execution from two witness rooms protected from the risk of ricochet by the bullet-proof glass.

The shooting was carried out in a specially designed execution chamber inside Utah state prison, a simple room measuring 6 metres by 7 metres (20ft by 24ft). Gardner was taken into the chamber shortly after midnight (7am BST), having spent his final hours sleeping, watching the Lord of the Rings trilogy of films and reading the thriller Divine Justice.

He was strapped to a black chair with a metal tray placed beneath it to collect his blood, had a hood placed over his head, and a white circular target pinned to his chest to mark his heart – the precise location of which had been identified earlier by a prison doctor.

Then five local police officers, chosen for their skills as marksmen and kept anonymous by law to minimise the risk of reprisals, were ushered into the chamber and lined up behind a brick wall at the other end of the room about 7.5 metres away. They were handed .30-calibre rifles, the muzzles of which they inserted through a gap in the wall to point at the condemned man.

Four of the rifles were loaded with a single live bullet. The fifth contained an "ineffective" round – which unlike a blank gives the same recoil as a live round; that way none of the five executioners know whether they delivered the fatal shot, thus lessening their psychological burden.

Gardner never disputed his guilt or sought to minimise the terrible acts he had committed. In 1980 he was convicted of robbery and sent to Utah state prison, where his life would end 30 years later.

In 1984 he escaped, and on 9 October, high on cocaine, he shot and killed a barman, Melvyn Otterstrom, at Salt Lake City's Cheers Tavern.

On trial for that murder, he made another escape attempt on 2 April 1985, arranging for a gun to be slipped to him by a female accomplice as he was being brought to Salt Lake City's central courthouse. In the melee, he shot a lawyer called Michael Burdell in the right eye. Burdell died in hospital 45 minutes later.

Burdell's family has consistently opposed the execution of Gardner. His niece, Donna Taylor, speaking to the Guardian outside the prison, said her uncle had always been against the death penalty. "He just didn't like the idea of killing anybody. He wouldn't have wanted this."