Colin Clarkson, 51, of Heneage Road, Grimsby, admitted carrying out the attack on his unsuspecting 19-year-old victim in front of horrified shoppers at Asda on Holles Street at 5.30pm on Wednesday, July 18.
He then calmly walked into the fruit and veg section and sat down on the floor to eat a punnet of raspberries.
When challenged by the store manager, he announced “I’ve killed someone” before taking a steak knife from his back pocket and slamming it onto a nearby conveyer belt.
He then waited calmly for officers to arrive and arrest him.
Clarkson was later deemed fit to stand trial and pleaded guilty to attempted murder and possession of an offensive weapon in a public place. He was sentenced earlier today at Hull Crown Court.
Luckily, his knife had not cut into his victim’s artery or windpipe and he escaped with a four inch cut to his neck.
However, he will have to live with the psychological impact of the ordeal for the rest of his life.
In his victim impact statement, the 19-year-old business and marketing student, who has asked not to be named, said the attack had left him a shell of the man he was.
He said: “I have grown a beard to disguise the injury – that way I don’t have to see it each time I look in the mirror or see a photograph.
“I tried to carry on as normal with work but I quickly found that I would suffer with flashbacks. I wasn’t in the right frame of mind.
“I was scared, jumpy and too nervous. I had to leave.
“I have never caused him harm. I had never met him and he has stolen so much of my life.”
Detective Constable Abbie Auckland, who led the investigation, said: “This was a really disturbing random attack, which his victim is incredibly lucky to have survived.
“CCTV shows that at about 5.30pm Clarkson was standing outside the store watching his victim going about his business.
“He stays there, watching him, for around 10 minutes before approaching him from behind as he deals with a customer.
“At that point you can clearly see the knife in his hand and then he attacks.
“What is most chilling is the way he then walks calmly away to the fruit and veg section and sits on the floor eating raspberries until he’s approached by the store manager.
“Luckily, attacks of this kind are incredibly rare. However, our thoughts remain with the victim and his friends and family, who will have to live with the consequences of Clarkson’s actions for the rest of their lives."
She thanked members of the public, store workers and the ambulance crew for their quick thinking and bravery.
She said: “Their actions meant that we were able to quickly arrest Clarkson at the scene and ensure that no-one else was injured.”
Clarkson was also told he will serve an extended five years on licence on his release.