Cole Allen, the suspect in the White House Correspondents’ Association Dinner shooting, will remain behind bars following a detention hearing on Thursday, as federal prosecutors laid out more video evidence in the attack.

U.S. Attorney for D.C. Jeanine Pirro posted a nearly six-minute video on social media Thursday that she said showed Allen “casing” the area of the Hilton Hotel the day before the April 25 dinner.

In the footage, a man is seen walking down a hallway and going into a gym on the night of April 24.

The footage also shows the night of the dinner and a man walking down the same hallway before charging through the Secret Service magnetometer checkpoint. A Secret Service member was shot during the incident, but the bullet hit the agent’s protective vest, officials said.

Pirro says the footage, which includes video where the playback speed is slowed down, shows Allen “shoot a U.S. Secret Service officer.”

“There is no evidence the shooting was the result of friendly fire,” she added.

Allen, 31, faces three felony counts of attempted assassination of the President of the United States, transportation of a firearm and ammunition over state lines with the intent to commit a felony and discharge of a firearm during a crime of violence. He has not entered a plea.

In an overnight court filing, Allen’s attorneys questioned what evidence the government has to determine Allen fired his weapon.

Prosecutors have said in documents that Allen fired the shotgun at least once as he ran past the magnetometers, and they said he fired “in the direction” of the Secret Service officer who was struck in the vest. Prosecutors said one spent cartridge case was recovered from the chamber and “at least one fragment was recovered from the crime scene that was physically consistent with a single buckshot pellet.”

Allen shot a Secret Service officer at “point blank range with a shotgun,” Secret Service Director Sean Curran said in an appearance on Fox News on Thursday afternoon.

“All the evidence I have seen, the suspect shot our officer point-blank range with a shotgun. Our officer heroically returned fire while being shot point-blank range in the chest with a shotgun and was able to get all five shots,” Curran said. 

Pirro told Fox News earlier on Thursday, “We know [Allen] fired off that 12-gauge shotgun one time.”

She said “the Secret Service officer fired his weapon five times” and she added that the agent did not shoot himself.

Pirro said Allen will face additional charges. She also said investigators are searching for anyone he might’ve threatened by name.

The California native — who was carrying a shotgun, a pistol and knives — was tackled by law enforcement after Saturday night’s gunfire inside the Washington, D.C., Hilton hotel, where thousands of journalists as well as President Donald Trump and members of his Cabinet were gathered for the annual dinner. Allen did not reach the ballroom, where the dinner was underway.

During his detention hearing on Thursday, Allen conceded to remain detained pending further legal proceedings in his case, his attorney said. Allen, dressed in an orange jail jumpsuit, appeared calm and did not speak during the hearing. He is set to return to court on May 11.

Allen’s Thursday court appearance came a day after federal prosecutors filed a detention memo, supporting their request for a judge to hold the defendant in custody pending trial.

“The defendant attempted to kill the President of the United States, Donald J. Trump. The crimes with which the defendant is charged are among the most serious in the United States Code, and the evidence of his guilt is overwhelming,” prosecutors wrote.

Under what prosecutors titled in court records as “The Defendant’s Assassination Plan,” prosecutors cited his writings in which he allegedly laid out his plan to target top members of the Trump administration, according to the memo. 

The suspect also sent a prescheduled email to his employer minutes before launching the attack, in which he allegedly apologized for his “unprofessionality [sic],” according to a pretrial detention memo prosecutors filed in federal court on Wednesday.

“Consider me to be submitting my resignation effective immediately (if it matters.),” Cole allegedly wrote in the email, according to the memo.

The tutoring company C2 Education, where Allen purportedly worked, said they are cooperating “fully” with law enforcement and denounced the “horrifying incident” at the correspondents’ Dinner, but omitted details of Allen’s work history. 

“We were shocked to hear the news of the horrifying incident that transpired at the White House Correspondents’ Dinner,” the tutoring company said in a statement on Sunday. “We are cooperating fully with law enforcement to assist them in their investigation. Violence of any kind is never the answer.”

Retired FBI Agent and ABC News contributor Brad Garrett said that in his decades of investigating major crimes, he could not recall another suspect submitting a job resignation letter in a screed.

Garrett, however, said he was not surprised the suspect submitted his notice. He said the resignation notice suggests it fits in with the “parallel personality” of someone who has led a responsible life, yet can also exhibit another side in which they are filled with anger and rage.

“It’s fairly common in the writings of mass shooters to apologize to people. The idea that you are telling your employer that you’re formally quitting kind of fits into that to a certain extent,” Garrett said.

ABC News’ Luke Barr and Bill Hutchinson contributed to this report.