Omar Mateen
A young Omar Mateen mugs for the camera in this undated photoReuters/handout

Orlando shooting gunman Omar Mateen is said to have made a series of Facebook posts before and during the attack at Pulse nightclub on 12 June. In his final post, Mateen warned that the US would see attacks by Islamic State (Isis/Daesh) within days, before he shot dead 49 people in the name of the terrorist group.

On 15 June, a letter from the Senate Homeland Security Committee to Facebook, revealed that Mateen had made a series of posts about Isis, as well as "the filthy ways of the west". The letter addressed to Facebook CEO Mark Zuckerberg requested further information on the gunman's online activity in light of the attack.

According to the letter from Homeland Security, Mateen posted on Facebook ahead of the attack: "America and Russia stop bombing the Islamic State... I pledge my alliance to Abu Bakr Al-Baghdadi... May Allah accept me."

Another post by the gunman stated: "The real Muslims will never accept the filthy ways of the west" and "You kill innocent women and children by doing us airstrikes... now taste the Islamic State vengeance."

Chairman of the Homeland Security Committee, Ron Johnson, said in the letter that his team had also found that Mateen searched for "Pulse Orlando" and "shooting" during the attack to find out if the media had begun covering his rampage. Additionally, the gunman had used Facbeook in May to search for information about the San Bernardino terrorists and in early June Mateen searched for "Baghdadi speech".

In a copy of the letter obtained by Fox News, Johnson said to Zuckerberg: "As the Committee examines the attack and considers legislative proposals to address homegrown extremism, I respectfully request your assistance with the Committee's inquiry given Mr Mateen's use of Facebook."

The Homeland Security Committee is requesting "all Facebook data" on Mateen, including but not limited to activity logs, timeline information, messages, photos and posts. It has also asked for Facebook staff to arrange a briefing with committee staff on the information available to Facebook prior to and during the attack at Pulse nightclub.