Moses Christensen appeared to have walked through a stream when he was detained by police at an isolated property near Shropshire's B4363 last August, Stafford Crown Court was told.
Jurors have been told they must decide whether the unlawful killing of 70-year-old Richard Hall near the summit of Brown Clee Hill was murder or manslaughter.
Christensen, of Corser Street, Stourbridge, West Midlands, is said by friends and family members to have appeared depressed and suicidal in the previous weeks, after abandoning plans to kayak around the UK.
On the second day of Christensen's trial, jurors heard evidence that the 22-year-old was wanted by West Midlands Police for making threats to kill, when Mr Hall was attacked on Thursday, August 13.
The first police witness in the trial, Pc Sam Bertie, said Christensen was taken to hospital after being found by officers outside the home of a woman who had called police.
The officer, whose bodycam footage was played to the court, said: "From my observations it appeared as though he had walked through a stream.
"It was as if he had sat in a bath - they (his clothes) were completely soaked."
The officer said Christensen made "numerous comments about having murdered someone" and was able to describe the knife used.
"He was very particular," Pc Bertie added. "He mentioned it was a serrated knife, it was a DK06 duct knife and it had a black handle."
Asked by prosecutor Adrian Keeling QC if Christensen had confirmed where the murder had taken place, the officer added: "Yes. On the top of the Brown Clee Hills."
The trial also heard from a resident who contacted police after Christensen rang her doorbell.
The woman told the court Christensen had politely asked her to call the police for him, saying he had committed a crime that he would like to admit.
During the conversation, the woman said, Christensen had seemed OK and was "very respectful".
The Crown alleges that Christensen was able to understand the nature of his own conduct, formed rational judgments and killed Mr Hall "because that is exactly what he wanted to do".
Christensen, who is said to have autism spectrum disorder and had previously spent periods of time living rough in the countryside, denies murder, by reason of diminished responsibility.
The trial continues.