The man murdered in his car in Co Down is believed to have been shot a number of times by somebody sitting in the back seat.
Speculation was also mounting that the murder could have been a case of mistaken identity, with another man the intended target.
Philip Strickland (36) was discovered on the Ballydrain Road, Comber, at around 9pm on Wednesday by passers-by who stopped to administer first aid. He died later in hospital.
While few details of the murder were released by detectives investigating the shooting, it is believed Mr Strickland was the victim of a possible feud between rival families.
It has been linked to loyalist tensions in the area and low level criminal elements.
Three men - aged 54, 26 and 25 - were arrested yesterday and taken to Antrim serious crime suite for questioning.
It is understood they are a father and two sons.
Mr Strickland was found in a front seat of his blue Citroen Saxo car on the quiet rural road in a picturesque part of Co Down.
There is a theory that his killer may have been in the back seat of the car.
Police are currently examining the vehicle for forensic evidence.
At a Press conference Detective Superintendent Brian Hanna was quizzed about the possibility of a family feud or mistaken identity being possible explanations for the murder.
He declined to comment on any possible lines of inquiry, saying it would be "inappropriate to speculate".
"We won't go into details of the investigation at this point in time," he said.
"We are following a number of lines of inquiry, it's such an early stage of the investigation it would be inappropriate to narrow it down to any single theory at this point in time.
"It's very early days so we are still keeping a very open mind as to the investigation to ensure we get the right outcome.
"Ultimately, what we have here is a 36-year-old man who has been killed and our thoughts at this time are with his family."
Detective Superintendent Hanna described the shooting as a "very vicious murder".
"In an area such as Comber, which has a very low crime rate, it's completely unexpected," he said.
Investigating police officers are keen to trace the drivers of a number of cars reported to have fled from the scene after the killing.
Mr Strickland is thought to have been a single man who lived in east Belfast.
The Ballydrain Road remained cordoned off throughout the day yesterday from Waddle's Hill.