A mother-of-nine and her nephew became innocent victims of a "vendetta of violence" when they were shot dead in their own home, a court has heard.
Annie Ekofo, 53, and psychology student Bervil Ekofo, 21, were allegedly killed by Obina Ezeoke at their flat in East Finchley, north London, on September 15 last year.
Silent "assassin" Ezeoke shot Mr Ekofo as he slept, then killed his aunt when she came out to investigate, the Old Bailey heard.
Opening the trial, prosecutor Mark Heywood QC said: "Soon after dawn in early autumn last, an assassin crept noiselessly into a second-floor family home.
"At first, none of the six people sleeping inside heard anything. Almost all were still asleep.
"The killer moved to his left and into a bedroom. There ahead of him was a young man, sleeping on a thin mattress on the floor under a duvet.
"For the killer, this was as good a target as he could expect, a young man of the house of just the right age.
"He crept forward, gun in hand. He raised the muzzle and placed it almost against the back of the sleeping dreadlocked head.
"And then, with a deliberation and purpose that was as much cowardly as it was murderous, he pulled the trigger."
After he had unleashed "hell" on the household, the mother of the family came into the hall dressed only in her underwear, jurors were told.
Instead of waving his revolver to scare her off, the killer raised the barrel and pulled the trigger for a second time, the court heard.
Mr Heywood said: "The Crown's case is that the cowardly killer is this defendant, Obina Ezeoke.
"He went there quite deliberately with a gun to attack and kill one of the young men of the family, one of those in their teens, as part of a vendetta of violence.
"His hate was such that he did not falter when confronted by a second person - he simply took her life as well.
"In fact, both lives were innocent. The young man he killed was a cousin, visiting at short notice, for one night only."
The prosecutor told jurors there was no doubt the execution-style killings amounted to murder but the "core question" would be whether Ezeoke was involved.
Ezeoke, previously of Cambridge Heath, east London, denies two counts of murder.
The court heard that a young granddaughter found Mrs Ekofo lying on the floor in just her knickers and with blood on her chest.
She cried out: "There's something wrong with Grandma."
Other members of the family alerted emergency services and tried to help Mrs Ekofo, who appeared to have a pulse and was trying to breathe.
It was only later that Mr Ekofo was found lying face down on the floor with a gunshot wound to the back of his head.
Both were pronounced dead within minutes just after 7am.