The two gunmen accused of targeting Jews at a Hanukkah celebration at Sydney’s Bondi Beach in an attack last week threw four homemade explosive devices—which didn’t end up detonating—into the crowd before they opened fire, authorities alleged in court documents released on Monday.

The existence of the devices is among several new details about the attack and the suspects, who authorities have identified as 50-year-old Sajid Akram and his 24-year-old son Naveed Akram, that are included in a police “facts sheet” that summarizes the allegations against the surviving suspect. The father and son are accused of killing 15 people and injuring 40 others at Bondi Beach on Dec. 14. Sajid Akram was killed at the scene. His son, who received medical treatment after being shot in the abdomen, is facing multiple charges, including murder, attempted murder, and terrorism.

The two men threw three pipe bombs and one tennis ball bomb into the crowd, according to the documents, which are partially redacted. While the devices didn’t detonate, authorities said preliminary analysis revealed them to be “viable improvised explosive devices (IEDs).” Authorities said it’s unclear at this time which suspect threw the devices into the crowd. Police found a fifth device that “appeared to be an IED” in the trunk of a car, which was registered to Naveed Akram and was parked in the vicinity of Bondi Beach. Officers also found two homemade Islamic State flags in the car.

Authorities believe the father and son “meticulously planned this terrorist attack for many months,” according to the documents. 

The documents said that “a number of relevant videos and images” found on Naveed Akram’s phone “indicated that he and his father … adhered to a religiously motivated violent extremist (RMVE) ideology.” Investigators found videos, including one recorded in October, in which the father and son can be seen sitting with an image of the Islamic State flag behind them. In the video, the two men “make a number of statements regarding their motivation for the ‘Bondi attack’ and condemning the acts of ‘Zionists,’” authorities alleged in the documents.

The documents referenced another video filmed in October in which the father and son seem to be training with firearms in the countryside. Police said they think the video was recorded in the state of New South Wales.

“The Accused and his father are seen throughout the video firing shotguns and moving in a tactical manner,” the documents said.

Authorities also pointed to CCTV footage that they said depicts two men “believed to be the Accused and his father” driving to Bondi Beach two days before the attack. The footage shows two men exiting the car and walking along a footbridge, from which the suspects allegedly opened fire the day of the attack.

“Police allege that this is evidence of reconnaissance and planning of a terrorist act,” the documents said.

Sajid Akram’s wife told police that she was under the impression that her husband and son were on a vacation in the south of New South Wales, according to the documents. She said that Naveed Akram called her each day from a payphone and shared what their plans were for the day.