Gardai probing the attempted hit on Lee Boylan have discovered a jar containing €9,000 buried in a field.
The find was made after detectives drafted in Army engineers to help them during a number of searches in the Hartstown area of west Dublin yesterday.
One of the places raided was a car wash once run by murdered Kinahan-linked criminal Eric Fowler.
The jar, stuffed with wads of €50 notes, was found in a nearby field.
The Defence Forces engineers used ground penetrating radar to locate the jar, which had been buried one metre underground.
As part of the operation, gardai also arrested three men aged in their 20s and 30s.
Searches by local gardai and members of the Armed Support Unit were also carried out in Limerick and one male was arrested there.
All four were last night in custody at Blanchardstown and Finglas garda stations, where they were detained under Section 50 of the Criminal Justice Act.
One of the men arrested is suspected of being the spotter who tipped off the gunman as to Boylan's movements.
Another is suspected of supplying a car used in the shooting.
The seizure and arrests were made as part of the ongoing investigation into the shooting of Boylan (24).
Boylan was shot multiple times in a horrific daylight attack as he sat in his van on the Blakestown Road on March 6.
He suffered gunshot wounds to his upper body and neck and has been left with life-changing injuries as a result.
Boylan is known to gardai, and a number of his associates have links to organised criminals, including the mob led by drug dealer 'Mr Flashy'.
However, he had no previous convictions himself.
His father, Noel Boylan, also survived an attempt on his life.
He was shot on June 1 in broad daylight outside a Lidl supermarket also on the Blakestown Road - just 450 metres from where his son was gunned down.
He was shot twice in the arm and chest in front of shocked onlookers and shoppers.
Sources said the elder Boylan remained conscious as onlookers rushed to his aid, and witnesses said that he had been shouting: "First they shot my son, leaving him paralysed... now they shoot me."
While Boylan was shot in the chest, it is understood the bullet missed vital organs.
He is recovering from his injuries.
However, sources have said that Lee Boylan's "life will never be the same again" following the devastating injuries that he sustained.
Gardai are probing links between the gun attacks on the Boylans and the murder of Fowler (34).
Lee Boylan is not considered a suspect in the Fowler murder. However, the killing has been blamed on associates of his who have links to the cartel.
Gardai previously received information that Fowler was blamed for the theft of €50,000 and suspect this may be the main motive for his murder.
A garda spokesperson last night said the searches in Hartstown and Limerick were part of an "ongoing strategy tackling organised crimes gangs".