Two of the gunmen were killed by the security forces during last Wednesday's attack, while a third is on the run, officials said.
The attack was the deadliest in Tunisia since the uprising which led to the overthrow of long-serving ruler Zine al-Abidine Ben Ali in 2011.
Suspects have been arrested over the attack but just two gunmen were thought to have raided the museum.
They are said to have been trained in Libya in an area controlled by Islamic State (IS) militants.