A US government court filing on Wednesday raised questions about officials’ initial assertions that a gunman shot a Secret Service officer while allegedly attempting to assassinate US President Donald Trump at the White House Correspondents' Association dinner.

The suspect, Cole Tomas Allen, 31, fired a shotgun "in the direction of the stairs leading down to the ballroom" where Trump, other administration officials, and members of the press were gathered on Saturday night, according to the pretrial detention motion, which offered the government's most extensive account yet of the incident.

In the motion, prosecutors referred to an officer firing five times, but the document does not mention that officer or any other being shot. A spent cartridge was found in the suspect's shotgun, according to Wednesday's motion.

The document did not accuse Allen of aiming at or striking the Secret Service officer who authorities say was shot in the chest but protected by his body armor.

That contrasts with statements made earlier by acting Attorney General Todd Blanche and Jeanine Pirro, the US Attorney for the District of Columbia. It also raises the question of who fired the round that struck the Secret Service officer.

Hours after the incident, Pirro told reporters that the suspect would be charged with "assault on a federal officer using a dangerous weapon," though that is not among the charges brought so far. Pirro has said Allen could face additional charges. Prosecutors did charge Allen with attempting to assassinate the president.

Blanche told ABC's George Stephanopoulos on Sunday that he believed shots from Allen's shotgun hit the officer. He reiterated that belief at a press conference on Monday, but added the caveat, "We're still looking at that."

A White House official referred Reuters to law enforcement when asked who shot the Secret Service officer. The Secret Service and the Justice Department did not immediately respond to a request for comment.

The government's account of the shooting was further probed by a Washington Post examination Wednesday of security footage the newspaper obtained, showing no indication in those images that Allen fired his weapon at all.

The examination found that a law enforcement officer had fired his pistol multiple times at the suspect as he raced through the checkpoint at the Washington Hilton hotel. At one point in the episode, which only lasted a few seconds, other security personnel appear to be in the line of fire of the officer as he shoots at the suspect running past.

While Wednesday's detention motion did not mention a Secret Service officer being shot, an earlier affidavit filed Monday in support of the criminal complaint did, but not who fired the shot.

The affidavit filed in the US District Court said that Secret Service personnel "heard a loud gunshot." A Secret Service officer wearing a ballistic vest referred to by the initials "V.G." was shot once, according to the affidavit, but it does not say by whom.

Officer V.G. fired multiple times at Allen, who was not shot but fell to the ground, the affidavit said.

Before his attack, Allen wrote in a manifesto, excerpted in court filings, that "in order to minimize casualties, I will also be using buckshot rather than slugs (less penetration through walls)."

When asked at Monday's press conference whether Officer V.G. was the only officer who had fired his weapon, Blanche said investigators were collecting evidence but that it was not an "exact science." He noted that buckshot in particular "scatters everywhere, and sometimes it just disappears."

Wednesday's filing included a photo that Allen took of himself in the mirror of his hotel room before the attack. In it, he is dressed all in black except for what appears to be a red tie tucked into his pants and armed with an ammunition bag, a shoulder holster, a sheathed knife, pliers, and wire cutters.