Mr McIlhagga, 42, was killed by a masked gang outside a house at Riverview Park in Ballymoney, County Antrim, on 3 January.
The Ballymena man was beaten and shot in the leg and died from his injuries.
The three men arrested on Wednesday are aged 24, 41 and 48. A number of other men arrested previously were released without charge.

On Monday, the BBC's Panorama programme uncovered several safety concerns, from staffing levels to waste storage.
The Mannin Branch of the Celtic League has called on the Manx government to campaign for a full, independent inspection of the plant in Cumbria.
Sellafield says the site is safe and has been improved with significant investment in recent years.
A spokesman added: "Safety is our priority and we are managing a very complex site which has got a great deal of hazardous radioactive materials on it."
The Isle of Man is located about 34 miles (55km) from the nuclear fuel reprocessing plant.
Due to its potential impact on the Manx fishing industry, the Manx government began monitoring radioactivity levels in the Irish Sea in 1989.
A government spokesman said: "Seafood fished in Manx waters can contain traces of radio-nuclides associated with effluent discharges from Sellafield to the Irish Sea, therefore these are monitored regularly to confirm that they remain well below maximum safe limits."
The BBC investigation was prompted by a whistle-blower - a former senior manager who was worried by conditions at the plant.
He said his biggest fear was a fire in one of the nuclear waste silos or in one of the processing plants.
The Manx government said it was particularly concerned about "the structural integrity of ageing waste storage ponds and silos".
A spokesman added: "However we are content that Sellafield Ltd and the nuclear regulators are trying to improve the safety situation.
"The government has asked questions about the technical solutions being developed to decommission these redundant structures and representatives have visited the site to look at the work under way".

The firm has reported a net profit of $471m (Â£294m) in the three months to 8 September.
China contributed more than half of Yum's $3.6bn revenue during the period.
US-based Yum is the biggest Western restaurant operator in China and fears about growth in the country had pushed Yum shares lower in recent weeks.
Profits in Yum's Chinese business had dropped in the second quarter because of higher costs but rebounded in the third quarter, rising by 22%.
Since June, the group has opened 394 new restaurants, of which 192 new units were in China, which contributed to its sales growth.
Globally, profits for the group grew 18% during the period.
The company beat its earnings targets and has raised its full-year outlook.
Police investigating the murder of father of five Brian McIlhagga last week have arrested three men.
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The Manx government is "concerned" about the safety of the Sellafield nuclear site, a spokesman said.
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Yum Brands, which runs the KFC, Pizza Hut and Taco Bell restaurant chains, has seen third quarter profits soar 23%, boosted by strong sales in China.