SOUSSE, Tunisia — The student who massacred holidaymakers on a Tunisian beach and at a swank resort hotel acted alone during the attack but had accomplices who supported him beforehand, an Interior Ministry official said Sunday.
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 being questioned in the capital, Tunis, Interior Ministry spokesman Mohamed Ali Aroui told The Associated Press.
The attacker has been identified as Seifeddine Rezgui, a 24-year-old graduate of Tunisia's Kairouan University where he had been living with the other students. The attack was claimed by the radical Islamic State group.
"We are sure that others helped, but did not participate," Aroui said. "They participated indirectly."
Investigators believe the suspected accomplices provided the Kalashnikov assault rifle to Rezgui and helped him get to the scene, Aroui said.
Authorities have yet to suggest a motive for the carnage. A security official close to the investigation said the student frequented an "unofficial" mosque in the Tunisian holy city of Kairouan for the past two years.
The official said a swimmer had found the attacker's cellphone in the Mediterranean. The phone showed the attacker spoke with his father just before his assault, the official said on condition of anonymity because he wasn't authorized to speak publicly.
Friday's attack on the Imperial Marhaba Hotel shook this 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 populate Tunisian beaches — and about what it may mean for their own countries in an age of globalized terrorism.
British counterterrorism police official Mark Rowley said Sunday that Britain has mobilized more than 600 officers and staff — one of the force's largest counterterrorism deployments in recent years — in response to the attack.
At least 15 Britons were among the 38 killed, the most serious attack on the British since 52 people were killed in attacks targeting London's transport network in July 2005.
Britain has deployed senior detectives and forensic teams to Tunisia.
Ballistic tests showed the bullets came from a single Kalashnikov, Aroui said, adding that the attacker was equipped with four ammunition chargers — all found by investigators. Aroui said each might hold 30 rounds.
Shortly after Friday's shooting spree, Aroui had initially said that two people were involved in the attack before backtracking. To some, the long duration of the assault — reportedly lasting nearly 30 minutes — and the high casualty count might indicate that more than one gunman was involved.
The attacker methodically moved from the beach to the hotel's swimming pool, reception and other areas. The death toll surpassed the 22 people killed in March at The National Bardo Museum outside Tunis — again mostly tourists, in a country known for its beaches and rich history.
Tunisian authorities moved quickly to bolster security for tourists and other vacationers. Interior Minister Mohamed Najem Gharsalli announced late Saturday the deployment of 1,000 extra police officers at tourist sites and beaches. Tunisia's tourism sector made up nearly 15 percent of the country's gross domestic product in 2014.
"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 currently a tourism police unit in vacation areas of Tunisia and numerous police wear civilian clothes.
Tourism Minister Selma Elloumi will meet with foreign ambassadors to lay out new security measures for tourists.
On the night of the attack, Prime Minister Habib Essid announced a series of measures, including closing 80 mosques not condoned by the state.
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 told the AP on Sunday that two armed security officers, one at the main entrance and one at the beach, would be provided by the state on July 1.
"Many of my English friends died. They have been visiting us for 10 years. They even visited me at home and ate Tunisian food," Torkhani said. He echoed numerous accounts from tourists and hotel employees of the bond between them. "They love me and I love them."
Andrea Rosa in Sousse, and Bouazza Ben Bouazza in Tunis, contributed to this report.