A person tried to carry a gun into the Farlam commission of inquiry in Rustenburg on Friday, causing the venue to be evacuated.
Commission spokesperson Kevin Malunga confirmed that police were questioning one person.
"There was a significant security breach and we can't leave anything to chance," he told reporters outside the Rustenburg Civic Centre.
"No witness... is allowed with a firearm into the building."
The gun was found with the use of security scanning equipment.
Malunga could not disclose further details as this would "defeat the purpose of the investigation".
The auditorium was declared safe again after a police sweep and the hearing resumed just before 11am.