A registered sex offender whose dismembered body was found in his bath was murdered in an act of "retribution", police have revealed.
Noel Brown and his daughter Marie Brown were both strangled in Deptford, south London in December 2017.
His killer is thought to have been Nathanial Henry, who was "linked" to a crime Brown had committed years earlier, the Met Police said.
Henry, 37, died from a drugs overdose several weeks after the murders.
The Met said it would have pressed the Crown Prosecution Service to charge Henry, had he been alive.
Detectives said Henry killed Brown in revenge for one of the 33 crimes he had been convicted of, which included serious sexual offences, burglaries and thefts.
He was jailed in 1999 before being released in 2004 and placed on the sex offenders register.
Marie Brown was murdered when she came to check on her father.
Police revealed Henry was one of more than 500 "nominals" who they conducted intelligence and criminal record checks on early in the murder investigations.
But, Henry did not have a police record and was not a priority for detectives.
It was only when DNA left at the crime scene that partially matched that of his father, whose profile was on the national database, that detectives were able to link him to the murders.
Further inquiries are taking place to unlock and examine Henry's smartphone.
Detectives say they need to rule out the involvement of anyone else in the murders, though they have no evidence to that effect.
At the time of the double murder, police said Brown's attacker had tried to dismember his body.
He was last seen alive on 30 November 2017, in a Paddy Power betting shop on Deptford High Street.
In a statement, Brown's daughter Sharon said her father was "a valued man and caring father" who had not deserved to die in such a "horrific way".
"This devastating loss has robbed us of his presence unfairly, made worse by the knowledge that no-one is being brought to justice for this crime," she said.
Marie Brown's half-sister Cassandra and her daughter Vanita said they were still in pain two years after her death.
"All Marie ever did was care for everyone... she constantly wanted to help people," they said in a statement.
They added: "It is a terrible thing that the evil in this world cost us something as innocent as Marie."