CHATTANOOGA — (CNN) They joined the Marines to serve their country, willing to go to dangerous lands out of a sense of duty, idealism and patriotism.

Ultimately, they died in Chattanooga, Tennessee.

Authorities are still trying to piece together why Mohammad Youssuf Abdulazeez killed four Marines at a Navy operational center in the southeastern Tennessee city, which is thousands of miles from any war zone but unfortunately not bloodshed.

Terrorism is being investigated as one possibility, especially considering that a military recruiting center was also shot at, though it was not immediately known if Abdulazeez had any connection to any known terrorist group.

Nor is it known if he had any link to the four people killed or the others wounded — one a sailor in “pretty serious condition” after surgery, according to a Pentagon official, and the other identified by a law enforcement source as responding Chattanooga police Officer Dennis Pedigo, who was shot in the ankle.

Whatever the motive, it’s clear that four families are hurting badly, as is the community at large.

“Each of these men who lost their lives had served incredibly well,” Tennessee Gov. Bill Haslam told CNN on Friday morning. “We’re heartbroken.”

The U.S. military has not named the wounded sailor or the slain Marines.

But social media, including a Facebook post from a brother, indicate that one of the dead is Thomas Sullivan, a Springfield, Massachusetts, native who was a Marine gunnery sergeant.

The flag in front of Springfield’s city hall was lowered to half-staff Friday morning in honor of Sullivan, city spokesman James Leydon said.

“They’re still trying to come to terms with it all,” Leydon said of Sullivan’s family.

John Sullivan, the owner of Nathan Bill’s Bar and Restaurant in Springfield, changed his Facebook profile picture to a split shot of his smiling brother in uniform and a black ribbon over the Marines Corps logo. The ribbon has the words “in remembrance,” and below it appears, “R.I.P. Tommy.”

The Facebook page describes the late Marine as a graduate of Cathedral High School who grew up in Springfield’s East Forest Park neighborhood and went on to become a gunnery sergeant.

“He was our hero,” one post states, “and he will never be forgotten.”

Skip Wells was another of those gunned down, according friends of his family.

A 2012 graduate of Sprayberry High in the Atlanta suburb of Marietta, Georgia, Wells was studying history at Georgia Southern University.

Many of Wells’ friends posted tributes to him on social media.

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