May 6 (UPI) -- A federal grand jury has returned an indictment adding an additional assault charge against Cole Tomas Allen, the man accused of attempting to assassinate President Donald Trump during an attack at last month's White House Correspondents' Association Dinner.

Allen, 31, of Torrance, Calif., was initially charged April 27 with attempting to assassinate the president, discharging a firearm with intent to commit a felony and transporting a firearm in interstate commerce.

On Tuesday, a fourth count of assaulting an officer or employee of the United States with a deadly weapon was added to the list of charges, according to the indictment.

"Today's indictment underscores a simple truth: there is evidence this defendant intended to assassinate the president and that he shot a U.S. Secret Service officer after he traversed the country with a cache of ammunition to accomplish his goals," U.S. Attorney Jeanine Ferris Pirro said in a statement.

Allen is accused of storming a U.S. Secret Service security checkpoint located a floor above where the annual White House Correspondents' Association Dinner was being held the night of April 25 at the Washington Hilton. Trump and other members of his administration were present.