A Jaguar Land Rover manager left two young sisters paralysed after smashing his company 4x4 into their father's car during a road rage chase, a court heard.
Andrew Nay was brought to justice with the help of dashcam footage from his victims' Vauxhall and witness accounts of his "absolutely ridiculous" right-hand turn across oncoming traffic.
The venue manager, who has worked for Land Rover as a lead off-road driving instructor, was seen laughing and smiling with his passenger moments before Katrina and Karlina Raiba, aged five and eight, suffered life-changing injuries.
A three-day trial at Northampton Crown Court heard Nay was tailgating and "bullying" a woman driving a Mazda people carrier before the smash on the A509 near Wellingborough.
Nay, of Harrier Close, Weldon, Corby, Northants, admitted four counts of causing serious injury by dangerous driving but denied chasing the Mazda before hitting the victims' Vauxhall Signum.
In evidence to his trial, Nay said he had noticed "nothing in particular" during his journey and was turning towards a garden centre in his three-litre Land Rover Discovery 4.
But Judge Adrienne Lucking QC rejected Nay's testimony, ruling that he crashed while chasing the Mazda.
Describing the evidence against Nay as overwhelming, Judge Lucking said he had "harried" the people carrier after being prevented from leaving a roundabout on the A14.
The judge told Nay: "I have heard evidence from a series of witnesses travelling in the same direction as the Land Rover.
"In each case there evidence was given in measured terms, without exaggeration. By contrast I found the defendant's evidence unconvincing and inconsistent."
Commenting after the court's ruling, Karlina and Katrina's parents, Roberts Raibais and Renate Raiba, said their lives had been "completely shattered" by Nay's actions and that no sentence would be enough.
The couple, originally from Latvia, suffered broken bones in the crash. They said in a statement: "Andrew Nay's reckless actions had devastating consequences for our two beautiful daughters.
"Katrina and Karlina were happy, active children and he has robbed them of that.
"We will never be able to forgive him.
"Every day they ask 'when will we start feeling our legs again?' They think it's going to get better and it's too hard to tell them."
Representing the family, Richard Langton, a serious injury specialist from law firm Slater and Gordon, added: "This is one of the most heartbreaking cases I have ever had to deal with.
"Nay was an experienced driver, yet his complete disregard for other road users has left two innocent children paralysed from the waist down.
"Because of him Katrina and Karlina face a lifetime of profound disability."
During the trial, witnesses said Nay's Land Rover was so close they could not see its headlights in their rear view mirrors.
The former local authority employee, who worked on the launch of the Land Rover Discovery 3, was driving within a car length of other motorists in heavy traffic on October 3 last year.
Motorist Fraser Hopes' Mercedes was undertaken by Nay as he waited to turn into the B547 near Little Harrowden.
Mr Hopes told the trial: "There were two gentlemen in the car. They looked to me as if they were smiling and having a joke, having a laugh."
Another witness to the crash, Leslie Miller, said of Nay's right-hand turn: "It was absolutely ridiculous. There was no reason why it couldn't have waited."
Nay was told an immediate custodial sentence will be at the forefront of the court's mind when he is sentenced on Friday.