A 79-year-old man was fatally stabbed by a stranger who walked into his family's home.
Gerald Wickes was visiting his ex-wife and son in Eyres Monsell, Leicester, when he was attacked by Daniel Rounce on 22 February.
Rounce, 18, was charged with murdering Mr Wickes but was deemed mentally unfit to face a conventional trial.
After a trial of the facts at Leicester Crown Court, it was found he did carry out the fatal attack.
Prosecutors told the hearing Rounce did not know Mr Wickes or his family, but entered the home in Queens Park Way through an unlocked door.
Rounce - who was 17 at the time - was "unannounced and uninvited" and stabbed Mr Wickes in the heart with a large knife when he was asked what he wanted.
Mr Wickes died about 30 minutes after the stabbing, despite the efforts of emergency services.
Leicestershire Police said Rounce then left the property but was arrested near Aylestone Road about six hours later.
The knife and two of his rucksacks were discovered in nearby woodland, the force added.
A jury on Friday determined Rounce to have committed the act of fatally stabbing Mr Wickes, and being in possession of an offensive weapon.
Rounce, of The Green, Markfield, was found not to have committed the act of assaulting an emergency worker at the time of his arrest.
He was remanded in custody and will appear before the court again on 9 February.
After the hearing, relatives of Mr Wickes, known as Ged, paid tribute to him.
His son Garry Wickes said: "I am so very proud to say that Ged Wickes was my dad.
"He will always be remembered by people as one of life's helpers. He would give you all the time in the world and could turn his hand to anything from DIY to helping in the garden or helping friends at home."
Det Insp David Greenhalgh, of Leicestershire Police, said: "This was a devastating incident which resulted in a 79-year-old man losing his life in a horrendous way because of the actions of a teenager who was unknown to him.
"We will never fully know why this happened and my thoughts very much remain today with Mr Wickes' family.
"They have lost a loving father, grandfather and great-grandfather."
