A man stabbed a stranger to death with a kitchen knife while out running near a children's playground, police said.
Glyn Rouse, 61, was attacked in Cherry Lane, Crawley, West Sussex, at about 10:30 GMT on 28 November 2017 and pronounced dead shortly afterwards.
Vladimir Ivanov, 23, of Juniper Road in Crawley had denied murder but pleaded guilty to manslaughter by diminished responsibility at Lewes Crown Court.
A hearing date for his sentencing has provisionally been set for 1 February.
Mr Rouse was attacked by Ivanov on a footpath close to the playground in Cherry Lane and discovered by passers-by with serious wounds to his neck, head, chest and left arm, Sussex Police said.
The pair were not known to each other, the force added.
Ivanov was found in the area shortly afterwards.
"He was covered in blood and had a wound to his left hand, believed to have been sustained during the attack," a police spokesman said.
During police interview, Ivanov told officers he had taken a knife from his home and put it in his jacket pocket when he went jogging.
There were a number of other people in the area at the time he stabbed Mr Rouse.
"Something in my mind told me to do this," Ivanov told officers.
Police said Ivanov's mental health had been assessed during the trial and the prosecution accepted a guilty plea to the charge of manslaughter by diminished responsibility.
Det Ch Insp Mike Ashcroft said: "His motive for killing an innocent man who was unknown appears to be borne from the mental state of the offender.
"Ivanov only moved to the UK from Bulgaria a couple of months previously, and he appeared to be settled at an address in Crawley and was employed with a local delivery firm."