The prison service and gardaí have launched separate investigations after one of the country's most feared criminals threatened the life of an innocent member of the public in a postcard sent from the country's highest security prison.

The Sunday Tribune understands that a major probe was launched after Brian Rattigan, the leader of one of the notorious Crumlin/Drimnagh feuding gangs, threatened a man whom he believed has got his former partner pregnant.

Rattigan, who is serving a life sentence for murder at Portlaoise prison, received a visit from his partner of 12 years, Natasha McEnroe, on 23 November. McEnroe informed the gang boss that she had met a new man and was leaving Rattigan for him.

Rumours are circulating that Natasha McEnroe is pregnant by her new man and Rattigan is livid at what he regards as his former partner's betrayal.

The pair had been together for 12 years and have a nine-year-old daughter. McEnroe had remained loyal to the gang boss even though he has been in prison for a variety of offences for nearly seven years. When she broke the news, Rattigan lost his temper and tried to assault McEnroe before being restrained by four prison officers and put in solitary confinement.

Two days later, gardaí received intelligence reports that a close associate of Rattigan made contact with a known hitman from Dublin 8 and said that Rattigan (29) wanted McEnroe's new lover dead and was prepared to pay any sum of money for it to happen.

Gardaí immediately offered the pair personal security advice and friends of the young couple have advised them to move abroad because Rattigan is so jealous and dangerous. The gang boss is understood to be very embarrassed that his long-term partner was cheating on him with another man and is afraid that he is being laughed at.

Last week, a postcard arrived at the 24-year-old man's house which had been sent from Portlaoise, prison sources said.

It said: "Dear XXX. Hope all is good with you and you have a Happy Christmas. Maybe the New Year might bring you something new. Enjoy it. From your friend, Brian".

Every letter that is sent from Portlaoise prison is checked by censors to ensure that no threats or inappropriate material is included and Rattigan, being aware of this, chose his words very carefully. Prison sources say the card was postmarked Portlaoise.

Nevertheless sources say that Natasha McEnroe's new lover got the message loud and clear, is extremely concerned about falling foul of Rattigan and is considering his options about where he will reside in the future.

It is understood detectives will quiz Rattigan about the alleged threats.

Last March, Nastasha McEnroe was arrested after the names and addresses of the jury that convicted Brian Rattigan for murder were found in an apartment where she was staying.

Gardaí found several confidential garda documents, including an intelligence bulletin that was stolen from a garda car, as well as the jury list.

After being quizzed for two days, McEnroe was released without charge. The jury list related to the murder of Declan Gavin in 2001.

Last December, Rattigan was found guilty of the murder of Gavin, who was stabbed to death outside a fast-food outlet in Crumlin. It was the first murder in the so-called Crumlin/Drim­nagh feud, which has claimed the lives of 16 people so far.

During the trial, there were attempts to intimidate witnesses and gardaí involved in the case. Judge Barry White commented on this when the verdict was handed down.

White was forced to jail one Rattigan associate for contempt of court after he turned up in court each day and stared at jurors and potential witnesses in what was blatant intimidation. Two gardaí were openly threatened with murder during the case.

Mick McCaffrey is the author of Cocaine Wars: Fat Freddie Thompson and the Crumlin/ Drimnagh Feud. He will present a four-part TV3 documentary on the book which begins at 9pm on Tuesday 4 January