A teenager fatally stabbed a pensioner through the heart after randomly walking into an unlocked house, a court has heard.
Gerald Wickes, a 79-year-old great-grandfather, died from a single blow inflicted as he was visiting his ex-wife and son at a house in Leicester on 22 February.
Prosecutors told a jury Daniel Rounce - then 17 - walked uninvited into the house in Queens Park Way, Eyres Monsell, stabbed Mr Wickes in front of his ex-wife and son and ran off within 90 seconds.
Rounce, now 18, is charged with murdering Mr Wickes, possessing a bladed article and assaulting an emergency worker.
He is currently the subject of a trial of the act after being deemed unfit to stand conventional trial due to his mental health.
A trial of the act is not to decide whether someone intended to commit an act or question a defendant's state of mind but to decide if they physically did it.
Prosecutor Steven Bailey told Leicester Crown Court: "The attacker walked in through an unlocked door, unannounced and uninvited.
"He walked into the room, he ignored their questions about what he was doing and he said very little, except words to the effect that he would decide what was going to happen next.
"The attacker pulled out from somewhere in his clothes a large orange knife and stabbed Mr Wickes in the chest, just once, but that was enough.
"The prosecution says that the attacker was Daniel Rounce."
Mr Bailey told the jury of five men and seven women that the defendant had gone missing from his supported accommodation in Markfield, near Leicester, the previous day.
A man, whom the prosecution says was Rounce, was seen on CCTV loitering in the Eyres Monsell area on the day of the attack, wearing dark clothing and a motorcycle helmet. He was also allegedly seen passing Mr Wickes' ex-wife as she walked home at around 4pm.
Over the course of around 45 minutes, he was then seen walking past her home several times, before launching his "random attack", Mr Bailey said.
Mr Wickes died around 30 minutes after the stabbing, despite the efforts of emergency services.
Mr Bailey said Rounce was arrested about six hours later, but "started to struggle and kick out" as he was detained, which led to him kicking an officer in the leg.
Mr Wickes' DNA was found in blood on the back of Rounce's glove, with police later recovering the knife believed to have been used in the attack after the defendant fled the scene, the jury was told.
Two bags of belongings - also seen on CCTV prior to the killing - were also found discarded, and contained a laptop that had Rounce's thumbprint on the keyboard, and other items which tied him to the scene, the court heard.
Rounce was not present for the first day of the court proceedings.
While the defendant cannot be criminally convicted, the burden of proof for a jury remains beyond all reasonable doubt.
Jurors will not deliver a guilty or not guilty verdict, but will instead only determine if Rounce physically did what he is accused of.
The trial continues.