On Michael Flynn, Attorney General Sessions says vetting can't 'catch everything'

— -- Attorney General Jeff Sessions said "you don't catch everything" in reference to the Trump transition team's vetting of former National Security Adviser Michael Flynn,

Flynn, who was fired early in his tenure by President Donald Trump, is under scrutiny for his dealings with Russia, including whether the former Army lieutenant general violated the law by accepting payments from foreign governments.

"We need to do a good job of vetting, but that’s a complex issue and I'm not sure anyone could be expected to find that," Sessions told ABC News' Amy Robach live on "Good Morning America" today.

"I’m comfortable that they’re working hard to do vetting. But it's obvious that often times you don’t catch everything that might be a problem," Sessions continued. "I don’t know the facts of this case; maybe there's an explanation for it."

Sessions' comments came one day after the White House appeared to try shift blame to the previous administration for the Trump transition team's approval of Flynn's security clearance.

Flynn was the director of the Defense Intelligence Agency under former President Barack Obama, but he was forced out of that role after two years and ultimately retired.

"His [security] clearance was last reissued by the Obama administration in 2016 with full knowledge of his activities that occurred in 2015," press secretary Sean Spicer told reporters Thursday afternoon.

Trump announced the appointment of Flynn as national security adviser in November 2016.

The president fired him in February after it was revealed that he allegedly he misled Vice President Mike Pence about the nature of conversations Flynn had with Russia's U.S. ambassador.

Documents released in mid-March showed Flynn was paid a total of $56,200 in 2015 by three Russian firms owned by or closely tied to the Russian government.

ABC News' Kelly McCarthy, Benjamin Siegel and Veronica Stracqualursi contributed to this report.