FBI: Motive for the July 16 attack in Chattanooga may never be revealed

FBI Director James Comey answers questions during a news conference at the FBI office in Nashville on Friday, Nov. 13, 2015.

NASHVILLE - The public may never know what motivated a 24-year-old Chattanooga man to kill four Marines and a sailor in an attack on Chattanooga's U.S. Naval and Marine Reserve Center last July.

Investigators have said Muhammad Youssef Abdulazeez was a homegrown violent extremist but have not offered more details about what motivated the attack that began at a military recruiting center and ended when Abdulazeez was shot to death by police who followed him to the reserve center.

"We're still trying to make sure we understand Abdulazeez, his motivations and associations, in a really good way," FBI Director James Comey told reporters during a visit to Nashville's FBI field office on Friday.

Comey said he understands the public interest in the shooting, but he did not know whether there would ever be a public report on it.

"Sometimes the way we investigate requires us to keep information secret. That's a good thing. We don't want to smear people," he said.

Comey also praised Tennessee for being one of 16 states that uses the National Incident-Based Reporting System to collect crime data.

"You and I can find how many books are sold on Amazon by any author, but we do not have similar capability at the national level with respect to crime," he said. That includes data about police use of force.

"I'm trying to get the entire country to move to be like Tennessee," he said. "My goal is to be at that place within five years, and we will have far better conversations in this country about crime."

One of the questions the FBI currently can't answer is why homicides have increased in many of America's large cities this year. "It's a complicated topic, but we really have to figure it out because people are actually dying," Comey said.

Speaking of recent outrage over sometimes deadly confrontations between white officers and black civilians, Comey said he wants his agency to contribute to a conversation that brings law enforcement and the communities it protects closer together.

Comey said it is important for officers to be able to imagine the perspective of a "19-year-old African American young man walking home from the library who has done nothing wrong and encounters one of us."