TYRONE native and multimillionaire Seán O’Neill was the classic example of an Irish immigrant success story – until his world collapsed when secrets from his past came back to haunt him.

A teenage conviction for membership of the IRA, immigration and tax fraud, weapons violation and even charges of bigamy have been levelled against him. A photo of him beside Sinn Féin leader Gerry Adams has done untold damage.

His downfall has been more spectacular than his rags-to-riches background and O’Neill is now facing up to 146 years in prison and fines of up to $4m (€2.8m).

It all began to unravel in June 2007 when armed FBI agents raided his expensive Philadelphia home and dragged him away in handcuffs. A respected member of the business community in the city, O’Neill had built up a multimillion-dollar empire from scratch. He was arrested in front of his family.

Before this pivotal moment, O’Neill’s life is America was considered a huge success. He left Coalisland, Co Tyrone, at the age of 23 with just the clothes on his back. That was in 1983. Within a couple of decades, he’d amassed a construction and restaurant empire worth millions of dollars. And had it not been for the actions of his son, O’Neill’s charmed life would never been scrutinised by the US authorities.

In 2006, O’Neill went on a weekend break with his wife Eileen. His son Seán Jnr did what most 17-year-olds do when their parents go away – he threw a party. But some time during the night, Sean Jnr found and began to mess around with his father’s gun.

This somehow ended with the accidental shooting of his friend Scott Sheridan, also 17. Police were called by his elder sister Roisin, who found her brother clutching his friend’s lifeless body in the driveway of their home.

Police searches of the house naturally ensued. But detectives found a lot more than they’d bargained for. Paperwork at the family home revealed that in 1977 when he was just 17, O’Neill had pleaded guilty to membership of Fianna na h’Éireann, the IRA’s youth wing.

They also found a couple of old photographs of O’Neill with Gerry Adams, taken in Ireland. After his conviction for membership of a terrorist organisation, he had failed to disclose his terrorism conviction in the US.

He then entered into a sham marriage with an American so he could stay in the country. When that marriage failed, he didn’t get a divorce before he married his wife in 1986, technically rendering himself a bigamist. He used a false identity on at least four occasions when he bought a gun to shoot squirrels, claiming to have been born in Texas and giving an incorrect date of birth.

But worse was yet to come. The FBI widened its investigation into this curious Irishman and a probe began into his business interests. It was revealed that he had failed to file personal tax returns between 2005 and 2007 and had paid some employees at his Maggie O’Neill’s Irish pub “off the books” to avoid paying $200,000 in tax.

At first, O’Neill defended himself vigorously. In court documents, the police were accused of “Irish Catholic prejudice” and it was said the allegation by police that Gerry Adams was an “IRA leader” was untrue in light of his role in the peace process.

But two months ago, O’Neill pleaded guilty to the immigration and tax-fraud charges as well as the gun charges. He is currently out on bail of $2.5m.

Just when it seemed like things couldn’t get any worse for O’Neill, they did.

Seán Jnr, fresh out of prison after serving nine months for the accidental killing of his friend, was put back into juvenile detention after violating his parole treatment programme. He had become involved in a violent altercation during which he had said he had “killed a better man for less” and had twice spent the night with a girlfriend, who is now pregnant.

Then his daughter Roisín (23), at three times over the legal alcohol limit, drove the wrong way down a motorway, killing a 63-year-old grandmother. She is awaiting trial for vehicular homicide.

Like her brother, she immediately got herself into even more trouble. She was caught in a car with underage youngsters a few months later, an open bottle of wine at her feet. Her brother was driving.

According to friends, O’Neill has somehow kept his spirits up despite an extraordinary fall from grace in just three years. The problems with his children have made his own legal situation the “least of my worries” he told Belfast newspaper The Sunday Life.

He will be sentenced on 8 ­October.