The student who massacred holidaymakers on a Tunisian beach and at a resort hotel acted alone during the attack but had accomplices who supported him beforehand, a Tunisian interior ministry official said yesterday.
Police were searching nationwide for more suspects after the slaughter of at least 38 people in Sousse on Friday, in Tunisia's deadliest ever such attack.
The attacker's father and three roommates were detained and questioned in the capital, Tunis, interior ministry spokesman Mohamed Ali Aroui said.
The attacker, Seifeddine Rezgui, was a 24-year-old graduate of Tunisia's Kairouan University. The massacre was claimed by the radical Islamic State (Isil) group.
"We are sure that others helped, but did not participate," Mr Aroui said. "They participated indirectly."
Investigators believe the suspected accomplices provided the Kalashnikov assault rifle to Rezgui and helped him get to the scene, Mr Aroui said.
Authorities have yet to suggest a motive for the carnage.
Ballistic tests showed the bullets came from a single Kalashnikov, Mr Aroui said, adding that the attacker was equipped with four ammunition chargers - all found by investigators. Mr Aroui said each might hold 30 rounds.
The attack on the Imperial Marhaba Hotel shook the North African nation that thrives on tourism and has struggled since its 2011 revolution to be the one Arab Spring country that succeeds in transitioning from authoritarianism to democracy.
The bloodshed shocked European nations across the Mediterranean worried for the safety of their citizens who holiday on Tunisian beaches - and about what it may mean for their own countries in an age of globalised terrorism.
Tunisian authorities moved quickly to bolster security. Interior Minister Mohamed Najem Gharsalli announced on Saturday the deployment of 1,000 extra police officers at tourist sites and beaches.
"We don't want to make tourist establishments into barracks. That's not our goal. But we must act to guarantee the security of the tourist sector," he said.
It wasn't clear whether the reinforcements would all be in uniform. There is a tourism police unit in resort areas of Tunisia and numerous police wear civilian clothes.
The owner of the Imperial Marhaba hotel, Zohra Driss, said unarmed beach guards "tried to beat (the attacker) with chairs, with flower vases of flowers, but it was impossible".
The hotel's beach security chief Lotfi Torkhani said yesterday that two armed security officers, one at the main entrance and one at the beach, would be provided by the state on July 1.