Along with the many other questions, some unanswerable, about the mass killings in Orlando is this: The murderer, Omar Mateen, was known by many – apparently including the FBI – to be dangerous.

Could anything have been done to stop him?

If so, why was he allowed to drop off law enforcement’s radar screen?

Hindsight often reveals to us that we were mistaken in dismissing certain people as harmless kooks.

Was there enough evidence Mateen was a ticking time bomb to have taken him into custody before he went on his murderous spree?

He had been investigated twice by the FBI in connection with his loyalty to the Islamic State terrorist group. In both situations, the agency did not find enough evidence to file charges against him.

He was known by some acquaintances and his ex-wife as a violent man, prone to fly into fits of rage.

Clearly, Mateen set off some alarm bells. But were they loud enough for law enforcement agencies to have taken any action against him?

In other words, should our foresight regarding Mateen have been closer to the hindsight we have now?

A serious discussion about how the system might have functioned better in this case may provide insights that will help us find ways to prevent future tragedies.