A Lewisham teenager has been found guilty of attacking a police dog, which he plunged a 12-inch hunting knife into while being chased.
The 16-year-old boy injured both German shepherd Finn and PC Dave Wardell when he ran from police in Stevenage, Hertfordshire, brandishing the "largest knife" the officer had ever seen.
Finn underwent extensive four-hour surgery after being stabbed in the body and head. The knife narrowly missed the dog's heart.
PC Wardell suffered a cut to his hand defending the animal.
The teenage defendant, who cannot be named because of his age, was convicted at Stevenage Youth Court of attacking the police officer and his dog, and possessing weapons.
The boy said he was acting in self-defence after fearing for his safety and being "bitten up" by the dog.
He claimed he only ran from police in the early hours of October 4 after becoming worried about being caught with the blade.
But district judge Jo Matson found the boy guilty of actual bodily harm, as well as criminal damage to the dog, and warned he could face jail when he is sentenced next month.
The judge said the defendant's evidence was "not credible or truthful".
She added: "His evidence does not add up. I do not accept that he found it necessary to take the actions he did to defend himself.
"He put himself in a position where it was necessary for Finn the police dog to stop him from running away with a knife in his hand.
"Stabbing a dog you know to be a police dog and lunging a knife at a police officer were not necessary or proportionate and I do not find he (the defendant) believed them to be at the time.
"PC Wardell gave very emotional evidence today and was clearly very distressed by what happened that day, and still is."
Addressing the youth, who had his mother by his side at court, the district judge said: "All sentencing options remain open, including custody."
Recalling the incident, PC Wardell said: "It was the largest knife I've ever seen.
"Finn didn't let go at all of the suspect. I was in fear of my life, and in fear of Finn dying in front of me.
"Finn is one of the highest trained dogs in the police force, I wished neither Finn nor myself were in that garden, but we were."
PC Wardell described the incident as “probably the most harrowing that's ever happened to me”.
The officer gave his backing to the introduction of Finn's Law, increasing sentences for criminals who attack working animals such as police dogs and horses.
The campaign had been supported by more than 100,000 people before the moves were halted by the announcement of the general election.
He said: "There is a campaign running and it will be down to the government of the day whether they make changes to the laws that currently exist."
Finn returned to the police duties after recovering from his ordeal, but has subsequently retired from service, Hertfordshire Police said.
Even though it happened outside their area, people in Kingston were so moved by the vicious attack on the dog and his handler that they made donations of toys and treats which were delivered by the local police.
The youth will be sentenced in Bromley next month.