THE FBI has released footage from the shooting at the Washington DC Navy Yard which left 13 people – including the shooter – dead.

The video from the morning of 16 September shows 34-year-old Aaron Alexis driving into the Navy Yard and then walking into the building armed with a shotgun. Alexis was able to enter the building as he was working as a contractor and had a valid pass.

The FBI said today there are “multiple indicators” that Alexis believed he was being controlled by low-frequency electromagnetic waves and was prepared to die in the attack.

A message found in his bag said: “Ultra low frequency attack is what I’ve been subject to for the last 3 months, and to be perfectly honest that is what has driven me to this.”

He had carved messages saying “End to the torment!”, “Not what yall say!” and “Better off this way!” on the weapon he used. The FBI said that he had bought a shotgun, ammunition and a hacksaw two days before the shooting.

The 34-year-old was a former reservist in the Navy who was working as a defence contract employee.

(Video: FBI/YouTube)

Alexis shot 12 people dead in the space of just over an hour before he was killed by police at the scene. The mass shooting was the deadliest on a military installation in the US since the Fort Hood shooting in Texas in 2009.

President Barack Obama said the shooting was a “cowardly act” and said military troops should not have to confront danger at home.

Around 3,000 people work at the sprawling complex, which oversees the building and buying of warships and combat systems for the US. The US Navy said on Monday that it wants more rigorous background checks to be carried out on all employees in future.

Timeline released by the FBI into the shooting on 16 September:

• 7:53 am – Alexis’ rental car, a blue Toyota Prius with New York licence plates, entered Parking Garage number 28 at the Washington Navy Yard, located directly across from Building 197.
• 8:08 am – Alexis exited Parking Garage number 28 on foot carrying a backpack. Alexis entered Building 197 and proceeded to the lift.
• 8:09 am – Alexis exited the lift on the fourth floor and entered the men’s bathroom carrying a bag and a clipboard.
• 8:15 am – Alexis crossed the hallway into the 4 West area of Building 197 with shotgun, but without the bag or a clipboard.
• 8:16 am – Alexis shot the first victim in the 4 West area of Building 197.
• 8:17 am – First 911 call is received from the fourth floor of Building 197.
• 8:20 am – Alexis left the fourth floor using the stairs and entered the third floor.
• 8:28 am – Alexis appeared on the first floor.
• 8:57 am – Alexis returned to the third floor.
• 9:25 am- Police officers shoot and kill Alexis on the third floor.

Aaron Alexis entered Navy Yard with a shotgun >

More details of ‘horrific’ Washington Navy Yard shooting emerge >

Washington Navy Yard shooter was former serviceman, police confirm >