The Dublin home of Gerry “The Monk” Hutch was raided on Tuesday by Gardai investigating the murder of David Byrne in a gangland feud.
Hutch heads one of two gangs involved in the feud which has resulted in three murders in recent months, two of them this month.
More than 100 Gardai, with an armed response unit on standby, carried out over a dozen searches on properties in north Dublin.
Byrne was shot dead at Dublin’s Regency Hotel at a boxing contest weigh-in by a gang of six, some disguised as armed police with AK47 guns.
Convicted criminal Byrne was reported to have been killed in revenge for the murder in southern Spain last September of Gary Hutch, The Monk’s nephew.
This month, three days after the Regency Hotel attack, Eddie Hutch, a brother of The Monk, was shot dead at his Dublin home.
Members of an international drugs gang headed by Dublin native Christy “Dapper Don” Kinahan, now based in Spain, are suspected of carrying out Eddie Hutch’s murder.
The Monk, who claimed several years ago that he retired from crime, was disguised in long grey hair at his brother’s funeral.
Detectives believe they have identified most of the men in the two Dublin shootings and are gathering evidence before making arrests.
Most of the gunmen are believed to be Dublin criminals but one is said to be a dissident Republican from near Strabane in Co. Tyrone.
The AK47s used in one attack are believed to have been stolen from the Provisional IRA 10 years ago.
Following the Dublin attacks, Gardai have stepped up security in the city, particularly in the Crumlin area on the south side and in the north inner city.