The FBI has been pressing Apple to open iPhones that belonged to a Saudi military student at a naval base in Pensacola, Florida.

The Saudi student took part in a shooting that left four people dead and several others injured.

On Monday, the FBI’s general counsel Dana Boente wrote a letter to Apple’s top lawyer, Katherine Adams, pressing the tech giant to grant access to the law ebfienforcement agency.

Even though the shooter is dead, the FBI, out of an abundance of caution, has secured court authorization to search the contents of the phones in order to exhaust all leads in this high priority national security investigation,Boente wrote in the letter.

Unfortunately, FBI has been unable to access the contents of the phones, the letter added, even after asking private technology experts if they could help agents crack them.

In the meantime, US officials decided to send home 21 Saudi military cadets after its probe finds last month’s fatal shooting by a Saudi officer as an act of terrorism.

Attorney General William Barr said on Monday the probe revealed the shooter was motivated by extremist ideology.

Saudi Lieutenant Mohammed Saeed Alshamrani, who was getting pilot training at Naval Air Station Pensacola, was fatally shot by the sheriff’s deputies..