A former inmate of the Serco-run Mt Eden Prison is seeking millions of dollars in compensation from the Corrections Department.
Benjamin Lightbody has been left brain damaged after being assaulted at the prison in 2013.
The Privacy Commission ruled Corrections interfered with his privacy by deleting or losing footage of the assault, he said.
Mr Lightbody, a former goldsmith, is seeking $5 million in compensation from Corrections for loss of earnings.
"Nearly a third of my brain has been damaged. I find it hard to sleep, eat regularly, my stamina and my overall health has decreased," he said.
Corrections said it could not comment at this time as there were still potential proceedings on the case.