But although a judge accepted the liquid thrown had never been analysed, she told Thomas when he appeared for sentencing that she had “some doubt” about his account, and that in her judgment he had taken “determined steps to prepare for his revenge attack” that day.
She also said that while the prosecution had suggested mixing an Oxo cube with the water would have increased the seriousness of any injury caused, they had not provided any evidence in support.
Maidstone Crown Court heard Thomas targeted his two victims in a laundry room on January 27 last year.
Having watched their movements from the prison landing above, he went into his cell and emerged less than a minute later carrying a bucket.
Inside it was a kettle which, having walked down a flight of stairs and to the laundry room door, he hurled at the two men, scalding their faces and bodies.
One, who suffered second-degree burns, later described hearing “a sizzling sound like bacon being put in a hot frying pan” and feeling immediate pain to his face and neck.
He required specialist treatment for his injuries, which included damage to his eyes, and remained in hospital for a week.
However, the court was told neither victim had supported the prosecution of their fellow inmate.
At the time, Thomas, formerly from Sidcup, was serving a 19-year jail term as part of a 27-year extended sentence imposed following his conviction for rape.
Other offences to his name include ones for violence committed between 2007 and 2010.
But at his sentencing hearing for the prison attack it was revealed that the “well-educated father” had served as a firefighter for a decade, and was awarded for his services in the aftermath of the four suicide terrorist bombings which rocked the capital’s transport network on July 7, 2005, killing 52 people and injuring more than 770 others.
His lawyer Tom Stern also handed photographs of his commendation to the judge.
Of the assaults themselves, Mr Stern explained Thomas had been the victim of bullying, which included having excrement thrown into his cell.
But he added that, having had his request to be moved to a different wing refused, he had acted “in the spur of the moment” on seeing the two men heading to the laundry room.
“The picture here is of a man who was simply at the end of his tether,” said Mr Stern.
“He wanted to be moved from the wing because of what was going on…and on the day [of the attack] he reacted in his stressed state.
“It wasn’t an act he had been harbouring for a length of time. It came to him that day and he took the moment, wrongly.”
Thomas had admitted two offences – one of causing grievous bodily with intent and one of inflicting GBH – at a previous hearing in October last year.
Jailing him for a total of four years, Judge Catherine Moore accepted he was regarded by staff as a “compliant prisoner” who did not cause trouble on his wing.
But she rejected the notion that he had acted “wholly impulsively” that day.
“Your attack was not an immediate response to any incident directed towards you or committed against you,” she told Thomas.
“This was an act of revenge, and you took determined steps to prepare for the attack and knew your victims were in a room with no escape.”
Under his extended sentence, Thomas cannot apply for parole until he has served 12 years and eight months of the 19-year jail term.
Judge Moore therefore ordered that the four-year sentence she had imposed should start from that point.
