Shortly after 8:30 p.m. on Saturday, an alleged assassin burst through a set of double doors one floor above a ballroom where President Trump and roughly 2,600 other White House Correspondents' Dinner guests were eating a salad course.

Seven seconds later, he was apprehended by federal law enforcement, multiple sources familiar with the matter told CBS News. 

After Cole Allen, the 31-year-old alleged assailant, used an interior stairwell to descend from his tenth-floor room at the Washington Hilton Hotel, he arrived at an elevator bank on the terrace level with a set of double doors to his left.

There, in a hallway out of view of security cameras, he removed a jacket that had concealed a shotgun, law enforcement officials told CBS News.

Authorities found the jacket there later, the sources said.

What followed was a rapid chain of events. 

A K-9 unit exited a security checkpoint through the double doors. Two seconds later, Allen came through the doors, turned left and — in another two seconds — sprinted through a magnetometer the U.S. Secret Service had been in the process of disassembling.

Two seconds after that, gunfire rang out. 

Secret Service Director Sean Curran said Thursday that from the evidence he had seen, the suspect shot at a uniformed officer. The officer "returned fire while being shot point-blank range in the chest with a shotgun, and was able to get off five shots" as he was falling, Curran said on Fox News.

The suspected gunman went down between the checkpoint and a staircase leading to the ballroom below. 

"It appears that the suspect hit his knee while being engaged by the officer on one of our magnetometer boxes and began to fall to the ground," Curran said. 

After placing Allen in handcuffs, officers moved him a short distance away to remove what appeared to be a tactical vest.

Authorities found multiple knives and a handgun in addition to the shotgun, according to court filings by prosecutors. 

The Secret Service officer was hit on his protective vest by buckshot from Allen's gun, officials said, and sustained some bruising. The suspect wasn't hit by gunfire. No one was seriously hurt. 

U.S. Attorney for D.C. Jeanine Pirro shared a video on X Thursday that shows the moment when the alleged assailant ran through the security checkpoint.

The distance between the security checkpoint and the ballroom staircase was about 40 feet, sources said. Had the gunman made it to the ballroom stairs, he would have had to navigate two sets of steps separated by a landing to reach the guests inside. 

"You're talking almost 355 feet from magnetometer to podium. That's almost 120 yards. That's a long distance to get to," Curran said. 

More than 30 federal protective details were working at the dinner, the sources told CBS News.

Allen has been charged with attempting to assassinate the president, transporting a firearm with intent to commit a felony and discharging a firearm during a violent crime. He has not entered a plea.

Mr. Trump told reporters Thursday: "They stopped the NFL running back. He was like a running back. In fact, if he ever got out, they're probably going to sign him. He was a speedy guy. But he was stopped."

The president said there's always room for improvement, but the Hilton where the dinner traditionally takes place is "a tough location" for security.