A father and son have been arrested by detectives probing the murder of Real IRA terror boss Alan Ryan.
In highly secretive operations, gardai arrested a crack cocaine dealer in his 20s this week -- a month after his taxi driver dad, who is aged in his 50s, was released from custody without charge after being quizzed for two days.
The dealer -- who is strongly connected to ruthless northside godfather 'Mr Big' -- is not suspected of murdering Ryan (32).
But gardai are investigating whether the 'mid-level' dealer was involved in carrying out surveillance on the terror chief in the days before the daylight murder.
The suspect has links to the Donaghmede area and was picked up in Dublin on Thursday.
It is understood that he left Ireland after Ryan's murder, but returned in recent days and was arrested by armed gardai.
Also in garda custody this weekend is a 38-year-old small-time north inner city criminal who has strong links to paedophile rapist Christy Griffin.
This suspect is known as a car thief and is understood to have had some involvement in the separate bitter north inner city feud that has claimed five lives.
A source said: "He is a reckless enough individual -- he may have helped the killers of Ryan after the murder. He was arrested on Wednesday.
"None of the arrested men was directly involved in the murder."
Mr Big, who comes from a respectable middle-class background and is well educated, has been striking fear into the underworld for years.
He controls a vast patch of drug territory stretching from Clontarf up to Drogheda, Co Louth.
The gang boss fled Ireland in March because of his feud with the Real IRA, but when Ryan continued to intimidate other major north Dublin criminals he put plans in place to have him killed.
The Herald has previously disclosed the structure of Mr Big's highly secretive organisation which consists of him at the head of the mob, with a veteran criminal now based in Co Cavan who introduced Tiger kidnappings to Ireland acting as his adviser.
Then he has five trusted lieutenants who look after the daily operations of the gang, as well as four thugs who carry out gun and pipebomb attacks for him.
Most of these criminals are now based outside the country in the aftermath of Ryan's murder.
Dissident republican Ryan was shot dead at Grange Lodge Avenue, Clongriffin, north Dublin, on September 3.
He was killed close to his home when two gunmen opened fire on him and one of his associates.
A car carrying what gardai believe were two gunmen pulled up and at least one of the passengers got out and started firing at Ryan and his friend Aaron Nealis, who was shot in the leg .
Ryan was hit a number of times, including as he lay wounded on the ground. He was shot at least once in the head by the masked gunman, who then ran back to the waiting vehicle and was driven off at speed.
Yesterday's arrests mean three people have been arrested so far in relation to the killing. His death is considered the most significant gangland hit of the year.
Just days after the murder, gardai arrested a middle-aged taxi driver from Donaghmede, but he was later released without charge. Sources said that this man was not directly involved in the murder.