The museum draws about 1.7 million visitors each year. It usually has guards inside and outside and other security measures in place because of its focus on the genocide of Jews in Europe during World War II and other more recent atrocities. All visitors must pass through metal detectors and their bags are screened.
Joseph Persichini Jr., head of the FBI's Washington field office, said his agents were investigating the shooting for possible ties to hate groups and domestic terrorism.
Persichini, Lanier and other authorities said they had no advance indications that the museum might be targeted. They said there were no indications that the shooter had any accomplices or other targets
"Preliminary indication is that this incident involved a lone suspect," Persichini said. "At this time, we have no additional intelligence information to indicate threats to area landmarks but will monitor the situation closely."
Von Brunn is "certainly the guy we're looking at, but we have to do fingerprints and do other work. We have to make sure and be absolutely positive," said another FBI official, who was briefed on the shootings but spoke on condition of anonymity because he was not authorized to discuss the investigation.
Visitors were evacuated after the shooting and the museum was closed for the rest of the day.
Abraham H. Foxman, the ADL's national director, issued a statement saying that the shooting at the museum "is a very sad and tragic event which reminds us ... where the spread of hatred can lead."
Foxman, a Holocaust survivor, said the shooting struck a particularly bitter chord among American Jews.
"That this, a place where people come together to understand what words of hatred do, should be the scene of hateful violence and loss of life is ironic and tragic," he said.
The Associated Press contributed to this article.
