A Co Tyrone man who became a millionaire after emigrating to the US 15 years ago is set to have an historic paramilitary conviction quashed in a move that might save him from deportation.

Sean O’Neill pleaded guilty in April to tax fraud and weapons charges, and is due to be sentenced by a Philadelphia court in July.

As a result the property tycoon’s citizenship is under investigation by the Department of Homeland Security, which is attempting to deport him back to Northern Ireland.

The court was told that the businessman failed to inform immigration authorities of a conviction for membership of Fianna na h’Eireann, the IRA’s youth wing, dating back to 1977 when he was just 17.

The family gained notoriety in the US after the Coalisland man’s two children appeared before courts accused of causing the deaths of two people in separate incidents.

Authorities also discovered that Mr O’Neill had married his wife Eileen without first divorcing an American woman who he wed in a sham marriage to gain residency in the US.

The discrepancies came to light after the family became embroiled in a series of high-profile incidents.

In 2006 police were called to the family’s Delaware County home after Mr O’Neill’s 17-year-old son Sean jnr accidentally shot and killed a school friend during a drunken party.

He was sentenced to detention in a juvenile facility after being found guilty of involuntary manslaughter.

During a follow-up investigation police searched the house and found gun silencers among Mr O’Neill snr’s possessions.

To add to the family’s troubles Mr O’Neill’s daughter Roisin (23) was charged with a driving-related homicide in September.

She was charged with causing the death of a 63-year-old grandmother after driving the wrong way on a motorway while three times over the drink-drive limit.

Last month the High Court in Belfast overturned historic convictions of two men, Joseph Fitzpatrick (48) and Derry man Terence Shiels (47), who were sentenced as juveniles in separate instances.

The court heard that in both cases the only evidence against the teenagers was confessions signed without the presence of a solicitor or an appropriate adult.

The ruling was hailed as a landmark decision that would open the door for other juveniles convicted through the Diplock court system to have their convictions quashed.

Madden and Finucane solicitors, who are representing Mr O’Neill in his appeal, have lodged an application to have the membership charge overturned.

If successful it could help save the millionaire from deportation from the US where he has lived since 1983.