Three people have been arrested over the killings of infamous malefactors Paul Massey and John Kinsella.
Massey, 55, was shot dead in 2015 and Kinsella, 53, from Rainhill, was fatally shot earlier this month.
A man,37, was arrested at Manchester Airport on suspicion of both killings.
A man, 48, is being caught on suspicion of plotting to kill Massey and a woman, 39, was apprehended on suspicion of helping a convict over the Kinsella killing, Greater Manchester Police said.
All three stay in imprisonment for interrogation.
Salford-born Massey, a security boss, and businessman was a sentenced malefactor once labeled “Mr. Big”.
Kinsella was a mafia authoritarian, said to have rescued erstwhile Liverpool footballer Steven Gerrard from a hoodlum.
Police carried out raids at dawn on Wednesday at addresses in the Heywood, Rochdale, and Salford areas of Greater Manchester and also in Cheshire as part of a joint operation between Greater Manchester Police (GMP) and Merseyside Police.
The victim’s families have been notified about the apprehensions, which are first made in connection with each killing.
Det Ch Insp Carl Jones, of GMP, said although each killing has an independent investigation, “we will continue to liaise with colleagues from Merseyside Police.”
Massey was murdered by a masked gunman in “military-style” clothes outside his Salford home on 26 July 2015, police said.
Many observers saw the gunman advancing towards the father-of-five at around 19:30 BST as he stepped out of his silver BMW at his home in Manchester Road.
Massey, incarcerated in 1999 for fourteen years over stabbing, unsuccessfully stood to be Salford mayor in 2012.
Kinsella was shot while walking his dog with his partner on a footpath near the St Helens Linkway near the M62 in Merseyside on 5 May.
His murderer was riding a mountain bike and shot at his partner as she fled from the scene, police said.
During a 2008 trial, Gerrard’s father said in a letter that Kinsella prevented a hoodlum from threatening his son.
Paul Gerrard described Kinsella as a “fixer” who had interfered when the hoodlum called The Psycho, had threatened to shoot the erstwhile footballer in the legs in 2001.