Traces of Giuseppe Miceli’s blood were found on a laptop case seized from murder suspect Mark Ellsom when he was arrested, a court heard.
The case of the computer was sent away for forensic investigation.
And the results showed there was a “one in a billion” chance of it not being Mr Micelli’s blood, a jury at Northampton Crown Court was told.
Mr Miceli, aged 71, died of head injuries some time between 11.10am on Friday, July 12, 2013, and 12.30pm the following day, at his home in Bants Lane, Duston.
Ellson, aged 41, formerly of Wellingborough, denies murder.
Giving evidence at the trial, forensic scientist Penelope Griffiths said the one in a billion figure was a “conservative estimate.”
She also said clothes seized from Ellsom were checked for blood, but none was detected.
Describing the crime scene, Mrs Griffiths said she found blood on the doorframes and doorhandles of the bathroom and lounge, but not the front door.
There was also blood on the floor of the living room, on the sofa, on an armchair, and on a number of surfaces.
Mrs Griffiths said that at various points after the attack, Mr Miceli had sat in his armchair; laid on his sofa and attempted to stem the flow of blood with a towel, as well as walking into the bathroom.
There was also blood on surfaces which would have been consistent with Mr Miceli being hit while he was on the floor, or slipping over and falling “extremely heavily,” Mrs Griffiths said.
Mrs Griffiths said it was not possible to ascertain what order these events occurred, although she could be sure each had happened.
Describing the DNA profiling, she said: “A sample was taken of the blood spots. Both were sent for full profiling, and both matched fully the blood of Giuseppe Miceli.”
Ellson denies the charge of murder. The trial continues.