The alleged gunman was running at full speed as he raced past the magnetometers on the second floor of the Hilton hotel in Washington, D.C. He discharged his shotgun, likely hitting the cellphone tucked inside the pocket of the bulletproof vest worn by the officer who fired five shots at him, according to two sources familiar with the investigation of the incident Saturday night at the White House Correspondent's Dinner.   

Officials investigating the incident said they estimated 31-year-old Cole Tomas Allen was running at about 9 miles per hour when he sprinted through and discharged the shotgun he had with him. Officials are still conducting ballistics testing to confirm whether it was the shot he fired that hit the officer wearing the bulletproof vest in the chest, sources said.

Allen tripped and fell to the ground, and officers immediately jumped on him, stripping him of his weapons and shirt to ensure he didn't have explosives on him, law enforcement sources told CBS News.

Meanwhile, one flight down in the ballroom, President Trump, first lady Melania Trump, the majority of the Cabinet and their spouses, and more than 2,000 journalists and guests were told to take cover. Some towards the back of the ballroom heard the gunshots and smelled the gunpowder, likely from the discharge of the shotgun.

Those closer to the front where Mr. Trump was sitting didn't necessarily hear the shots but quickly became aware of the disturbance. Most climbed underneath their tables for cover as Secret Service agents whisked the president and first lady away.

Allen was charged with attempting to assassinate the president of the United States and discharging a firearm during a crime of violence. He travelled to Washington from his home state of California by train, carrying two firearms and several knives, officials said. He is also charged with transportation of a firearm and ammunition with the intent to commit a felony. 

Charging documents quote from an email he sent to family members Saturday night stating that he wished to target administration officials "prioritized from highest ranking to lowest."

He appeared in federal court on Monday for a brief initial hearing wearing a blue jumpsuit, flanked by U.S. Marshals. Attorneys for Allen did not respond to requests for comment. Allen has not yet entered a plea. 

Officials tell CBS News that Allen was able to get so close to the event because he'd booked a room in the hotel and took an unguarded back stairwell from his hotel room 10 floors up.  

U.S. Secret Service Director Sean Curran told CBS News that the hotel, which is open to the public, and the ballroom were two separate locations and that the ballroom was secure.  In a statement released to the public late Saturday night, Curran said, "Tonight we saw exactly what our brave men and women do each and every day." 

Officials familiar with the investigation but who were not authorized to speak publicly said Allen was stopped by of a combination of his fall and because officials were able to jump on top of him to subdue him quickly.  

An eyewitness told CBS News he fell right in front of her as she took a phone call at the top of the staircase, just a short flight up from the ballroom. 

One source familiar with the investigation said investigators are looking at whether he fired the shotgun just before, during, or just after falling. Officials are also investigating whether the power from the shotgun blast caused the suspect to falter.  

A total of six shots were fired, one by the suspect with his shotgun, and the other five rounds by the Secret Service officer who was shot in his bulletproof vest, a source familiar with the investigation told CBS News. The officer was not seriously injured. The officer was not seriously injured. No other rounds were fired by other officers in the area, according to the officials with knowledge of the investigation. 

The incident prompted White House Chief of Staff Susie Wiles to meet with the Secret Service director to offer support to the agency, according to officials familiar with the meeting.