WASHINGTON — A law enforcement official says James Von Brunn, an elderly white supremacist, is being investigated as a potential suspect in the shooting today at the U.S. Holocaust Museum.

Another law enforcement official said Von Brunn's vehicle was found near the museum and was tested for explosives.

The two officials spoke on condition that they remain anonymous.

An elderly gunman opened fire with a rifle inside the crowded museum today, gravely wounding a security guard before two other officers returned fire. The assailant and his victim were both hospitalized.

The assailant was in critical condition, said Washington, D.C., Mayor Adrian Fenty.

D.C. Police Chief Kathy Lanier said the gunman appeared to have acted alone. He was "engaged by security guards immediately after entering the door" with a rifle, she said.