The DHS said the suspect, 29-year-old Rahmanullah Lakanwal, entered the US under an Afghan resettlement scheme, Operation Allies Welcome (OAW).
The scheme was launched in August 2021 under the Biden administration to resettle "vulnerable" Afghans after the Taliban takeover of Afghanistan in the same year.
"They came in, they were unvetted, they were unchecked", said President Trump, who called a reporter "stupid" for asking why he blamed the Biden administration for the Washington attack.
In an FBI news conference, the agency's director Kash Patel claimed the previous administration "made the decision to allow thousands of people into this country without doing a single piece of background checking or vetting".
And in a press release on the day of the attack, the DHS said the suspect "is one of thousands of unvetted Afghan nationals let into the country under the Biden administration's Operation Allies Welcome program".
On X this week, Vice President JD Vance recalled comments he made in 2021 "criticizing the Biden policy of opening the floodgate to unvetted Afghan refugees".
He made similar remarks about vetting failures in an interview with CBS earlier this year. Vance highlighted the case of an Afghan national, also evacuated to the US after the Taliban takeover, who was later charged with terrorism-related offences.