Dean Stansby, 41, was stabbed in the abdomen in Ancaster Road, Ipswich, on 8 February. He died in hospital and police are treating the case as murder.
A 23-year-old man was arrested on suspicion of murder, conspiracy to murder, and being concerned in the supply of Class A drugs.
A second 23-year-old was questioned on the same drugs charge.
Two others, aged 24 and 27, were also held on the drugs charge and suspicion of conspiracy to murder.
All the men, from London, have been released while police investigate. Four other men are currently on bail.
Four men arrested over a fatal stabbing in Suffolk have been released while inquires continue, police said.