Hundreds of uniformed law enforcement officers filed into a memorial service Thursday for an FBI agent who was shot to death last week, possibly by his own colleague, while pursuing suspected bank robbers in New Jersey.

Mourners entered an arts center here to view the body of Special Agent Barry Lee Bush. A funeral was to begin in the early afternoon, and he was to be buried in this eastern Pennsylvania community where he was raised.

About 200 Pennsylvania state police, dressed in black overcoats and olive green uniforms, marched under an overcast sky in military formation toward the service.

Thousands of mourners, including Attorney General Alberto Gonzales and FBI Director Robert S. Mueller III, were expected for the funeral on the campus of a private school.

Mueller was scheduled to deliver the eulogy for Bush, who played a key role in several high-profile cases during his 19-year FBI career.

Bush, 52, was fatally shot April 5 while he and other agents tried to capture a group of suspected bank robbers in Readington Township. The FBI said Bush may have been accidentally shot by another agent during the confrontation outside a PNC bank.

He was the 51st FBI agent killed in the line of duty.

"He had the demeanor of the type of guy that would be an FBI agent," said retired Pottstown Sgt. Paul H. Campbell, who was Bush's supervisor for a year when Bush was a patrolman in the 1980s.

An internal investigation into the shooting is under way. The FBI said Bush may have been struck when a fellow agent's weapon discharged accidentally. The FBI has declined to provide specific details.

However, two law enforcement officials with knowledge of the investigation told The Associated Press that the shooter may have mistaken Bush for a suspect. The officials spoke on the condition that they remain anonymous because they were not authorized to talk about the investigation.

Bush, who lived near Easton, Pa., was born in Pottstown and was a 1972 graduate of Pottstown High School. He is survived by a wife and two children.