A former top FBI official who was one of 10 signatories to a letter to Congress about the border crisis earlier this month warned that the open border between the U.S. and Mexico under President Biden presents the "greatest security risk in our lifetime."

Former FBI Assistant Director for the Criminal Investigative Division Chris Swecker told Fox News on Monday the letter he signed was meant to be an apolitical but blunt assessment of the multiple security threats President Biden's open border presents to the homeland.

Swecker warned that allowing millions of undocumented and unvetted foreign nationals to flow into the country renders useless the nation's intensive inland security framework.

"This open border, 1,800 miles of open border, represents the greatest security risk in our lifetime. And we can shut the front door or guard the front door, if you will, at airports and train stations and other modes of transportation, but if we just open up our border, all our intelligence agencies, all that work goes for nothing because we don't know who's coming in," Swecker said.

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"We have no idea and no way of vetting. There are 800,000 gotaways. We have close to 2 million migrant encounters."

Swecker and his fellow signatories also warned of a potential attack similar to the October 7 Israeli massacre by Hamas terrorists, given how there is little or no information on the backgrounds of the foreign nationals being released into the interior.

"It is stark to say so, but having a large number of young males now within our borders who could begin attacking gatherings of unarmed citizens in imitation of 10/7 and at the behest of a foreign terror group must be considered a distinct possibility... the warning lights are blinking," Swecker and his former FBI colleagues wrote to top lawmakers in national security or leadership roles.

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Swecker's letter was sent to House Speaker Mike Johnson, R-La., Senate Majority Leader Chuck Schumer, D-N.Y., House Intelligence Committe Chairman Mike Turner, R-Ohio, Senate Intelligence Committee Chairman Mark Warner, D-Va., Rep. Mark Green, R-Tenn., and Sen. Gary Peters, D-Mich.

The dangers of the open Mexican border also led a handful of House Democrats to side with Republicans and support a January 17 resolution denouncing Biden's policies and condemning the burgeoning crisis.

Fourteen Democrats, including border-state Reps. Colin Allred, Vicente Gonzalez, Henry Cuellar of Texas and Reps. Mary Peltola, D-Alaska, Greg Landsman, D-Ohio, and Yadira Caraveo, D-Colo., crossed the aisle on the measure.

On "America Reports," Swecker further warned that when so many gotaways are able to disappear into the interior, there is no way to surveil or vet them, presenting an "unacceptable level of risk" to the country.

"We know that [Iran-backed Lebanese terror group] Hezbollah and other terrorist organizations have been infiltrating into this country for a long time… all it would take is two or three trained professionals to conduct a devastating attack in the United States – I mean, catastrophic," he warned.

The former G-man underscored that most Americans are in favor of legal immigration and that his concerns are not political, but strictly in regard to national security concerns.

"All the security measures that we've taken since 9/11 are totally compromised because of this open border," he said