The confession made to a magistrate in the Usindiso arson case is admissible in the trial at the High Court in Johannesburg.
The trial within a trial on the matter has concluded at the court.
Seventy-six people died in the August 2023 blaze allegedly started by Sithembiso Mdlalose.
During the Khampepe Commission of Inquiry, the accused said he started the fire at the hijacked Marshalltown building to cover a murder he had committed.
Mdlalose also confessed to a Johannesburg magistrate in January 2024 that he started the blaze, but now in the trial, he says he was not of sober mind.