Both leading up to and during his deadly assault on Orlando night club Pulse, Omar Mateen accessed his Facebook account. He posted threatening status updates, and searched for key words relating to the tragedy, according to a Senate committee head briefed by law enforcement. Now, that Senator wants to know if Mateen's social media activity could have been used to prevent the attack.

Facebook declined to comment about the Orlando incident, which itself is unsurprising given that it's an ongoing investigation. But the company has been clear in the past about what it does and does not do to assist law enforcement in potential terrorist cases. Its systems are among the best, analysts say, at flagging and removing content that's potentially terrorism-related. But the balance between vigilance and censorship isn't easily attained. And even a more extreme posture, at least in this case, likely wouldn't have helped.

Suspicious Activity

In his letter Thursday to Mark Zuckerberg, Senator Ron Johnson (R-WI) detailed Mateen's Facebook activity the night of June 12, when he would go on to take 49 lives with a Sig Sauer MCX assault rifle and Glock 17 handgun. The content of his posts, and trajectory of his searches, are both alarming and upsetting.

"The real muslims will never accept the filthy ways of the west," Mateen wrote. "You kill innocent women and children by doing us airstrikes..now taste the Islamic state vengeance." He finished his string of posts with a particularly chilling missive: "In the next few days you will see attacks from the Islamic state in the usa."

Johnson, who heads the Senate Committee on Homeland Security and Governmental Affairs, further reveals that Mateen conducted searches on the site for a speech by ISIS leader Abu Bakr al-Baghdadi in the weeks prior to the attack, and had previously "used Facebook to conduct frequent law enforcement and FBI searches, including searching for specific law enforcement offices."

It's quite a revelation, one that has prompted Johnson to ask Facebook to provide all of the data the company has about Mateen's online activities, as well as "the information available to Facebook prior to and during this terrorist attack."