Two men, aged 35 and 46, have been arrested on suspicion of conspiracy to murder and remain in police custody for questioning.
It follows the death of 28-year-old Michael Blake, who was found with a gunshot wound to his leg and a gunshot wound to the back of his head on Manchester Road, Westhoughton, on Thursday, November 3.
Three men have already appeared in court charged with the murder of Mr Blake. They were Joe Wilson, 26, of Brinnington, Stockport; Nathan Quigley, 30, of Cleworth Walk, Hulme; and Nathon Aaron Daniels, 27, of Nottingham Avenue, Stockport.
A 27-year-old man arrested on suspicion of conspiracy to murder was released on bail until Friday, December 16 and a 52-year-old woman arrested on suspicion of assisting an offender has been released on bail until Wednesday, January 25.
Anyone with information is asked to contact police on 101, quoting incident number 2426 of November 3, or Crimestoppers, anonymously, on 0800 555 111.