Italian police say they have arrested a Moroccan suspected of taking part in the March attack on the Bardo National Museum in Tunis in which 21 foreign tourists, including an Australian, were killed.

Abdel Majid Touil, 22, was arrested on an international warrant by Italy’s anti-terrorism DIGOS police in the northern town of Gaggiano, officers told a press conference on Wednesday.

Touil, who is wanted for premeditated murder, kidnapping and terrorism, was detained on Monday evening. He was living with his mother, a carer, and two older brothers in the town near Milan.

• Friends mourn Tunisia victim

The Bardo attack on March 18 killed 22 people, including a Tunisian policeman, 28-year-old Australian-Colombian dual national Javier Cameloan and his Colombian mother, three Japanese, two Spaniards, a British woman, a Belgian woman, two French, a Pole, a Russian and an Italian.

Tourists getting off buses outside the museum were gunned down by two black-clad gunmen with automatic weapons, who then took hostages inside the building.

Many people were shot in the back as they tried to escape. After rampaging through the museum for several hours, the two gunmen were killed in an assault by security forces.

Tunisia’s President Beji Caid Essebsi said a few days after the attack that a third gunman was on the run.

Police said Touil had been in Italy before the attack. They said he entered illegally in February with a boatload of 90 migrants, before being issued with an order to leave.

The officers did not specify whether he had been expelled or, if he had, where he had gone to.

They said investigators had been able to trace Touil because his mother had reported his passport missing.

Authorities in Tunisia have arrested nearly two dozen suspects in connection with the attack and fired senior police officials over alleged security failures.

On March 29, Tunisian forces killed nine men allegedly belonging to the jihadist group accused of being behind the shooting, the Okba Ibn Nafaa Brigade.

Lokmane Abou Sakhr – an Algerian who allegedly masterminded the attack – was killed along with at least eight others from the notorious brigade.