One of the questions that has come up in the wake of the Orlando terror attack is why the FBI failed to stop Omar Mateen despite investigating him for possible terror connections on two occasions. It seems the answer is that there was simply no evidence, at the time, he was planning any specific attack.

Having an open investigation on Mateen gave the FBI freedom to perform surveillance and collect recordings of what he was saying. So why close his case at all? Given that Mateen’s name had been raise twice in connection to terrorism, why not leave his case open to allow more evidence to accumulate over time? It seems the answer to this question has to do with FBI investigative policy which sets a limit of 6 months on an open investigation. Time magazine reports:

Mateen first came to the FBI’s attention in 2013, when he was a security guard and co-workers heard him say he had connections to al Qaeda and Hezbollah, and that he hoped to martyr himself in a confrontation with the law, according to Comey. The FBI opened a preliminary investigation, which allows agents to conduct limited surveillance and searches, but not to use its most aggressive tools (like FISA or Title III warrants)…

Preliminary investigations of terrorist suspects can run for six months in search of evidence the person is a member of a terrorist group or is planning a specific terrorist attack. The agent on the case can get a six-month extension if he or she thinks there might be more to find…In Mateen’s case, the FBI got one extension of the preliminary investigation, then closed the case after a total of ten months.

It was only two months after the first preliminary investigation was closed that Mateen’s name came up again in connection with an al Qaeda suicide bomber who was originally from Florida. Catherine Herridge is reporting today that Mateen’s connection with the bomber may have been closer than the FBI suspected:

The relationship between Orlando terrorist Omar Mateen and an American suicide bomber in Syria was much “deeper” than previously understood by federal investigators, according to a government source.

Fox News was told the relationship as well as the Mateen case in general are “very complex” but would not go further, citing the sensitivity of the FBI investigation and classified information. The source said the bomber’s return to Florida in 2013 is under fresh scrutiny as well.

So it’s possible the FBI missed something but the simple answer to the question ‘why did the FBI close the investigation?’ is that agency guidelines encouraged them to do so:

Murphy, the FBI’s former number two who worked with then-FBI general counsel Valerie Caproni in revising the bureau’s investigative guidelines, says they discourage agents from monitoring potential terrorists over the long-term. Those guidelines retained the requirement that any preliminary investigation that did not produce evidence of a crime must be closed after six months. “Someone should have been monitoring [Mateen’s] social media 24/7,” Murphy says. “but under the guidelines that is not allowed,” he says.

Senator Lindsey Graham believes the problem is with the FBI’s approach to cases of potential Islamic radicalism. From Fox News:

“The FBI closed this file because the Obama administration treats radical Islamic threats as common crimes. I am not trying to solve a crime. I am trying to prevent an attack and if we kept the file open and we saw what he was up to, I think we could have stopped it,” Graham said, adding the focus would be on the suspect’s actions. “I am not suggesting he be followed because he is a Muslim. I am suggesting that he be followed because of what he did and what he said.”

FBI Director Comey has been reviewing the the previous investigation of Mateen. Comey said Monday, “I don’t see anything, in reviewing our work, that our agents should have done differently.”