Sartin's appearance at Durham Crown Court yesterday was his first in public since the remand hearings that followed his arrest for the murder of Ken Mackintosh, a British Telecom manager, and the attempted murder of 16 others, seven years ago.
The case was delayed because Sartin, 22 at the time of the shootings, was deemed unfit to plead until now. During that time he has lived at Ashworth Hospital, Merseyside, and was flanked by staff as he stood in the dock wearing a dark jacket with pale flecks and a plain tie.
Before Mr Justice Kennedy brought the episode to an end by sending Sartin to a secure unit for life, the apology, handwritten on lined notepaper, was read to the court by defence counsel, James Chadwin QC.
It said: "Apologising for the terrible offences I carried out on April 30 1989 will not help the family of the innocent man I killed or ease the memories of all the people I hurt.
"What I want my victims and the family of Mr Mackintosh to know is that their awful pain was not the result of a planned or intended crime and there was no pleasure involved.
"It was completely the product of a mental illness so severe that reality was taken over by insanity.
"All I want to say to everyone involved in this tragedy, the people on the legal side, the police, my family and all whose lives I affected is, I am so very sorry."
When the charges were read out earlier, Sartin, in a quiet faltering voice, replied: "Not guilty by virtue of insanity."
David Robson QC, for the prosecution, then told how on Sunday 30 April 1989 Sartin left his home with his father's double-barrelled shotgun and some ammunition and a knife.
His first two shots were fired at Judith Rhodes, 43, who was driving along the road. One shot smashed her windscreen, the other wounded her left hand.
Sartin then went on to shoot at five more people before seeing Mr Mackintosh, 41, who was walking home from a service at a nearby Methodist church. He shot him with both barrels from 20 yards and then let off another double blast at short range.
Mr Robson said Brian Thoms, 39, was among the other people shot as he rode his bike. He was seriously injured and managed to struggle to the safety of a nearby house.
Sartin was finally arrested in a pub car park.