Mottram, formerly of Bradford and now living in the Sheffield area, was convicted of arson following a trial at Bradford Youth Court in August 2024.
His barrister, Verity Barnes, told the court he had become a “reformed character” since the offence and had “matured considerably”.
The court heard Mottram used Greenman’s mobile phone to record footage showing his co-defendant kicking pieces of polystyrene onto the flames.
Judge Robinson said Dalton Mills was historically important and noted that businesses based at the site had suffered losses of about £130,000 as a result of the fire.
“The word used in the opening was gutted and that would seem to be appropriate,” he said.
The judge said he was satisfied Mottram had neither started the fire nor added combustible material to it, and accepted he had been led by Greenman, whom he described as the principal offender.
Greenman, 19, was due to be sentenced alongside Mottram, but his case was adjourned until February while a pre-sentence report is prepared.
Dalton Mills has since been the scene of several further fires, including a major blaze earlier this year which led to the evacuation of residents from nearby properties.
Bradford Council has previously said it has been working with Historic England and the Crown Estate on measures to improve security at the site.
