– As neighbors and friends tried to understand why a lone gunman launched two brazen attacks on military sites that left four Marines dead, investigators searched for terrorist ties but so far had found none, authorities said.

Knoxville FBI Special Agent in Charge Ed Reinhold told a late-night news conference that authorities had no leads linking the gunman to international terrorist organizations.

“There is no indication at this point that anyone else was involved,” he said late Thursday.

Although federal officials identified the gunman as Mohammod Youssuf Abdulazeez, there were several other spellings in his school and other records. The 24-year-old engineer, described by friends as hard-working and deeply religious, died during the attacks that also injured at least three people, including a city police officer.

Abdulazeez lived in Hixson, an upscale neighborhood in the northern section of the city. Many homes in the quiet cul-de-sac where he lived flew U.S. flags at half-staff as a memorial to those who died in the attack that began Thursday morning and lasted about half an hour.

“They were long-standing, good neighbors - just great people,” Mary Winter, 32, head of the Colonial Shores Neighborhood Assn., said of the Abdulazeez family. They attended Fourth of July cookouts and other regular festivities, she said.

“He just seemed like a very nice, very polite boy,” she said. “We don’t know what happened. Everybody is very shocked.”

So was Chattanooga’s Muslim community.

“This has just completely blindsided us,” said Dr. Azhar S. Sheikh, a board member of the Islamic Center of Greater Chattanooga. “Our thoughts and prayers are with the families of the victims. We share their sorrow.”

Although Abdulazeez grew up in Chattanooga, he had been living in Nashville in recent years, Sheikh said. Only in the last few months had he returned to live with his parents. “He kept to himself. But that’s how he’d been since I’d known him. Our acquaintance was fleeting. We are very shocked.”

The center practices “a comprehensive, balanced view of Islam,” according to its website. “We strive to embody the ‘middle path’ to which our scriptures call us, a path of moderation, free of extremism, and representative of the Islamic vision of a healthy community.”

Sheikh said the center monitored potential radicalization of its members, but had not had a problem. “We as a community, if we suspect anything like this, we approach the authorities,” he said. “We offered the FBI our unconditional support. We’re all struggling to connect the dots.”

Many members of the center fear that Muslims will be singled out in retaliation, Sheikh said. “That is a concern: Will there be any acts of reciprocity? We all have families, we all have kids.”

The president of the Islamic Society of Greater Chattanooga offered condolences.

“We are tremendously saddened by today’s shooting in our home town of Chattanooga, Tennessee,” Bassam Issa said in a statement Thursday. “Our hearts are with the families of the brave Marines who died today” and with those who were injured. “We condemn this act in the strongest possible terms as one of cowardice and hate.”

Abdulazeez was born in Kuwait, but was believed to have become a U.S. citizen. He went to school in the Chattanooga area, eventually earning a college degree as an engineer.

“He would always crack jokes in class, he always had the witty comment to add to what the teacher had to say,” said Kagan Wagner, a former classmate who now lives in the state of Washington. “But he made great grades, and being the funny guy never really affected him in a bad way.”

In sixth grade, Wagner recalled having a Bible history class with Abdulazeez, who ended up making a better grade than she did in the class. She also sat next to him in her ninth-grade geography class. “He was always really nice to me,” she said. “He was that kind of person. He’d say, ‘Hey, how are you doing’ and stuff.”

Wagner also said that Abdulazeez had a pretty big group of friends. “He was always smiling, telling jokes, he was never isolated in any way,” she said. She added that he was active in sports and the arts, appeared in the yearbook several times, and was never the subject of bullying.

“Him being Muslim was an afterthought,” she said.

Abdulazeez wrestled for most of his time at Red Bank High School, said his former coach, Kevin Emily, who now lives and works as a teacher and coach in Waterloo, Iowa.

“Mohammod was very humble. He always did what I asked him to do, he never gave me any problems,” Emily said. “All the guys seemed to like him. He was not an outsider.”

Abdulazeez stayed out of trouble and followed his faith closely, Emily said, sometimes taking breaks from practice to play or excusing himself for occasional religious events.

Emily recalled that Abdulazeez was popular and had many friends, including some at other high schools.

One summer, in an effort to get to know his wrestler better, Emily asked Abdulazeez about his faith and his background. “He was open with me, in talking about everything. I never got any indication of anger or resentment or anything out of it.”

When Emily began receiving phone calls and text messages from former team parents and wrestlers Thursday, he said he couldn’t believe it.

“I just sat there in my car, just stunned,” he said. “There was nothing out of the ordinary. He came from a good family. I don’t understand what went wrong with him.”

The attack began about 10:45 a.m. Thursday at a recruiting center on Old Lee Highway in Chattanooga where five branches of the military have adjoining offices in a strip mall. The gunman unleashed a barrage of more than two dozen rounds, but no one was injured, officials said.

With police giving chase, the gunman drove to the Navy and Marine Corps Reserve Center on Amnicola Highway, about seven miles away.

Upon arriving, the assailant jumped out and “almost instantly” started firing, a federal official said, leaving the four Marines dead and three others injured.

The attacks coincided with this week’s end of the Muslim holy month of Ramadan, a time when Islamic extremists have targeted rival sects in past years and Islamic State militants have sought to strike symbolic blows against Western enemies.

U.S. Atty. Bill Killian said the attacks were being investigated as an “act of domestic terrorism,” though no ties to terrorist groups had been established.

The Council on American-Islamic Relations, or CAIR, the nation’s largest Muslim civil rights and advocacy organization, said it condemned the attacks “in the strongest terms possible.”

“Such inexcusable acts of violence must be repudiated by Americans of all faiths and backgrounds,” CAIR Executive Director Nihad Awad said. “The American Muslim community stands shoulder to shoulder with our fellow citizens in offering condolences to the loved ones of those killed and injured and in rejecting anyone who would harm our nation’s safety and security.”