There is still no hard evidence of a terrorist plot against the Russian passenger plane that fell out of the sky and crashed into the Sinai desert on Saturday.  But U.S. and British intelligence sources are saying they may have linked a worker at the Sharm el-Sheikh airport to an ISIS bomb plot.

CNN:

"This airport has lax security. It is known for that," the official said. "But there is intelligence suggesting an assist from someone at the airport. "

Egyptian authorities, who are leading the investigation into the crash, haven't publicly responded to reports on U.S. intelligence. Since the crash, they've downplayed the possibility that terrorism could be involved.

The signs pointing to ISIS, another U.S. official said, are partially based on monitoring of internal messages of the terrorist group. Those messages are separate from public ISIS claims of responsibility, that official said.

In an audio message from ISIS' Sinai branch that was posted on terror-related social media accounts Wednesday, the organization adamantly insisted that it brought down the flight.

"Find your black boxes and analyze them, give us the results of your investigation and the depth of your expertise and prove we didn't do it or how it was downed," the message said. "Die with your rage. We are the ones with God's blessing who brought it down. And God willing, one day we will reveal how, at the time we desire."

Typically, ISIS is quick to trumpet how and who carried out any attacks for purposes of praise and propaganda. To some, the fact that ISIS hasn't provided details in this case raises doubt about the group's repeated claims of responsibility.

Officials in Egypt and Russia have said there's no evidence to support ISIS' claims.

"That was a very baffling way to claim credit for what would be the most significant terrorist attack since 9/11," CNN terrorism analyst Paul Cruickshank said.

"But there may have been a method behind this and a reason behind this, and that may have been to protect an insider at Sharm el-Sheikh airport."

Russia has grounded its entire Metrojet fleet, saying that "additional safety checks are being conducted."  British officials have halted flights from the Sharm el-Sheikh airport, citing concerns for the safety of British nationals.

Why did authorities so quickly rule out terrorism as a cause of the crash?  When ISIS first claimed responsibility for bringing down the aircraft, their assertion was dismissed as "ridiculous."  In fact, authorities bent over backward to make it absolutely clear that terrorism was not a factor.

Now, just a few days later, we learn of our intel community's suspicions about a worker at an airport with lax security who may have facilitated the smuggling of a bomb on board the Russian jet.  So why does the word "terrorism" get caught in so many people's throats?

First, there's the prospect of alarming the flying public.  The civil aviation industry was nearly destroyed in the year following 9/11, and no one wants to panic people about air travel.

But beyond that, some governments – ours included – think that identifying an incident as a terrorist attack will lead to hate against Muslims.  There's no evidence for it, of course, but some governments are apparently so frightened of being seen as "intolerant" that they will play down the possible terrorist angle to any attack – until they're forced to conclude otherwise.

The plane crash may turn out not to have been a terrorist attack.  But it would be good to see a little more honesty in public pronouncements next time when tragedies like this occur.