All four were charged with terrorism. One appeared to be barely conscious during Sunday's hearing.

The men are from the Central Asian republic of Tajikistan, which borders Afghanistan.

The massacre happened in an auditorium on the outskirts of Moscow as a crowd gathered for a sold-out rock concert. People in their seats heard what sounded like fireworks. At least four men with automatic weapons had begun firing repeatedly into the crowd. Then they set the concert hall on fire.

ISIS-K—the terror group's affiliate in Afghanistan—was quick to claim responsibility for the attack. The same group is also responsible for the killing of 13 US service members during the botched pullout from Afghanistan.

Russian President Vladimir Putin claims the men were headed to Ukraine where persons there were preparing to let them cross the border, but ... Kamala Harris told ABC that's not true.

"There is not whatsoever any evidence and in fact what we know to be the case is that ISIS-K is actually, by all accounts, responsible for what happened," Harris said.

US leaders are very concerned with the possibility that a similar terrorist massacre could happen here in the US or against Americans overseas.

Florida Senator Marco Rubio told ABC's This Week, "They'll do it here in the homeland. And I think we should be very concerned as the FBI director confirmed to me that ... there is a trafficking network out there that specializes in moving people. They do it for profit, moving people and migrants around the world, including across our southern border who have links to ISIS."

The head of the US Border Patrol Jason Owens, when asked in a CBS interview if he's concerned, answered "Absolutely. You ask any law enforcement officer, especially somebody that works in border security, that is what keeps us up at night. If we don't know who is coming into our country and we don't know what their intent is, that is a threat and they're exploiting a vulnerability that's on our border right now."

Former FBI Special Agent Eric Caron told CBN News he's especially concerned about America's ports, where Customs and Border Protection physically inspects only 3 percent of incoming containers.

"We have 328 ports of entry into America. They all have to be secure, and many of them are soft," Caron said.

He says last year there were over 1,000 joint terrorism task force cases related to sleeper cells and terrorism in the US. Subscribe for free to Breaking Christian News here

Dale Hurd: Since joining CBN News, Dale has reported extensively from Western Europe, as well as China, Russia, and Central and South America.

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