Pascal Kelly, whose gang murdered Real IRA terror boss Alan Ryan, managed to remove an electronic ankle tag.
The 48-year-old is now believed to be hiding out in the south of Spain.
Kelly is on bail while awaiting trial in Northern Ireland for money laundering.
PSNI officers had told a court that he was a leader of a criminal gang and a serious flight risk. They claimed he had access to a false passport and large quantities of cash.
He was arrested with another man last February when officers seized more than €65,000, 24 mobile phones and two cars.
After several unsuccessful attempts he was finally granted bail in recent weeks but has now absconded.
He claimed he was going to live in Ballyjamesduff, Co Cavan. Garda are aware of his disappearance but do not believe that he has returned to his native Coolock.
Sources say that he ripped off electronic tags that had been placed on him before donning a disguise to flee the country. It is understood that he managed to board a shipping container.
Kelly's girlfriend has not been seen at her home for weeks, leading to underworld speculation that she is with him now. They are most likely in Spain's 'Costa del Crime' where he has many associates.
In another sinister development the Herald can reveal that Kelly is friends with a well-known detective who became associated with his gang after his daughter became involved with them.
A source said: "Kelly has built up a number of relationships over the years. He will use his contacts carefully."
THE SINISTER BRUTE, WHO IS ONE OF IRELAND'S MOST SERIOUS CRIMINALS, HAS A HUGE NETWORK OF INTERNATIONAL CONTACTS AND IS WANTED BY POLICE ON BOTH SIDES OF THE BORDER.
After many attempts he was finally granted bail in the North subject to him wearing the electronic tag.
In February, Fermanagh Magistrates' Court heard that Kelly and a pal, who cannot be named for legal reasons, were arrested in a car on Enniskillen's Queen Elizabeth Road.
Kelly is also facing charges in this jurisdiction for threatening to kill a garda. He has previously survived two murder attempts and has more than 30 convictions for offences including robbery, burglary and drugs.