Three times over the past month, shots have been fired in the vicinity of top U.S. officials.

The latest shooting occurred Saturday evening, when a gunman approached the White House complex, took a gun out of a bag and opened fire before being shot and fatally wounded by Secret Service officers.

A bystander was also struck by gunfire, Secret Service officials said. No details were provided on the person or the severity of the injuries. No officers were wounded, the Secret Service said.

President Trump, who was in the White House at the time, thanked the Secret Service and law enforcement officers for their efforts and described the gunman as having “a violent history” and a “possible obsession” with the White House.

Here’s what we know:

Who is the shooter?

The gunman was identified by two officials with knowledge of the investigation as Nasire Best, 21, and was taken to a nearby hospital, where he was pronounced dead.

Mr. Best was arrested last July for walking into a restricted area on the White House grounds and ignoring signs and commands to stop. At that time, according to an affidavit filed in D.C. Superior Court, Mr. Best was already known to Secret Service personnel “for walking around the White House complex inquiring how to gain access at various entry posts.”

He was involuntarily held that June for blocking a vehicle entry on the east side of the White House, the affidavit said. At the time of that arrest, on a misdemeanor charge of unlawful entry, he had no pending warrants. He told officers at the scene that “he was Jesus Christ and that he wanted to get arrested.”

Court records show that a judge issued a “stay away order” the day of Mr. Best’s arrest, apparently barring him from the area around the White House. After he did not show up for a hearing in August, a bench warrant was issued.

Where did the shooting take place?

The shooting occurred a little after 6 p.m. near 17th Street NW and Pennsylvania Avenue, at the northwestern corner of the White House grounds.

What occurred at the White House when shots were heard?

The gunfire, which could be heard on several news feeds, prompted a brief White House lockdown and rattled the reporters who were gathered on the North Lawn.

The reporters were hustled inside the White House to the press briefing room.

What did President Trump say following the shooting?

In a social media post, Mr. Trump appeared to renew his push for a proposed ballroom and security expansion at the White House, saying the episode underscored the need for “the most safe and secure space of its kind ever built in Washington.”

What were the other shootings in the past month?

On April 25, a man armed with a shotgun, handgun and knives charged past a security checkpoint at the White House Correspondents’ Association dinner, where Mr. Trump was due to speak, and exchanged fire with Secret Service agents. The man, from California, was arrested and charged with attempting to assassinate the president.

On May 4, a man from Texas was wounded during an exchange of gunfire with Secret Service officers near the Washington Monument. He faces three federal charges, including assaulting federal officers with a dangerous weapon.