Dale Cregan has pleaded guilty to murdering father and son David and Mark Short in Greater Manchester last year.
Cregan, 29, has already admitted to killing police officers Fiona Bone and Nicola Hughes in a gun and grenade attack in Hattersley, Greater Manchester in September 2012.
Mark Short, 23, was shot at the Cotton Tree pub in Droylsden on 25 May 2012. His father David, 46, was killed in a gun and grenade attack on 10 August in Clayton.
Cregan originally pleaded not guilty to all four murders at Preston Crown Court. During the trial for the murders of the Shorts, prosecutors described his not guilty pleas as "bizarre".
Nicholas Clarke QC told the court it was "the worst kept secret in Strangeways" that Cregan had killed the pair, adding he admitted it to his mother.
He also pleaded guitly to the attempted mudrer of John Collins, Ryan Pridding and Michael Belcher, who were in the Droylsden pub at the same time.
In April Anthony Wilkinson, 38, who was one of Cregan's co-accused in the murder of David Short, also changed his plea to guilty.
Cregan changed his plea to guilty on the fourth day of trial in the murder case of PCs Bone and Hughes in February.
The officers were ambushed by Cregan after responding to a bogus call about a burglary at an address in Hattersley.
Clarke added the murder of David Short was "essentially" the same as the attack on the police officers a month later.
Clarke added: "Essentially it was the same way. The surprise ambush, the hail of gunfire and the gratuitous throwing of his calling card (the grenade)."
In his closing speech, Simon Csoka QC told the jury: "You now know for sure that he has murdered four people and that he has attempted to murder others inside the Cotton Tree pub.
"Ordinarily in a closing speech the defence barrister will tell you how important your task is, how it makes so much difference, how the liberty of the defendant hangs in the balance.
"All of those words mean nothing now, absolutely nothing.
"He is going to be sentenced for four murders and three attempted murders. He is not going anywhere. He is going to die in prison."
It is alleged the murders were the result of a long-standing feud between two rival Manchester families - the Shorts and the Atkinsons.
The other men still on trial for the murder of the Shorts are Luke Livesey, Damian Gorman, Jermaine Ward, Matthew James, Ryan Hadfield, Leon Atkinson, Francis Dixon and Mohammed Ali.
Atkinson, 35, from Ashton-under-Lyne; Livesey, 27, from Hattersley; Gorman, 38, from Glossop; Hadfield, 28, from Droylsden and James, 33, from Clayton are all accused of the murder of Mark Short, and the attempted murder of three others (John Collins, Ryan Pridding and Michael Belcher) at the same time.
Dixon, 37, from Stalybridge and Ward, 24, are accused of the murder of David Short, as well as the attempted murder of Sharon Hark on the same day and a single charge of causing an explosion.
Cregan denies the attempted murder of Sharon Hark.
Ali, 32, from Chadderton, denies assisting an offender.