An avid bicyclist, Kyle Hickman rode to see a friend on Saturday, a special education teacher named David Draa who had been struggling with memories of his combat service in Iraq. The two rode together, went back to Draa’s apartment in Takoma Park and hung out well into the night.

What unfolded over the next several hours ended in the most horrible way, according to interviews Monday with law enforcement officials and friends of Hickman. Some time before 2 a.m., the 30-year-old walked out of Draa’s apartment to repair his bike, apparently because he wanted to go home. Draa, 30, came outside as well, approached Hickman from behind, shot him, knelt over his friend’s body and turned the gun on himself. Police have classified the shootings as a homicide and suicide.

“This is a very tragic situation,” Takoma Park Police Chief Alan Goldberg said. “Kyle Hickman was a good friend, and through no fault of his own, a victim in this incident. David Draa, up until that morning, had been a respected and well-liked teacher.”

Hickman worked as a special education assistant in schools, his friends said.

Goldberg said officials probably will never know exactly what happened or why. But he said detectives think Draa “had experienced severe trauma” during his tour of duty as a U.S. Marine and had gone through difficulties in his personal life. Draa’s family couldn’t be reached for comment. A close friend of Hickman’s said Hickman had spoken of Draa’s struggles after Iraq and that Hickman was trying to help Draa.

“It was well understood among our friends that he had issues,” the friend, Clint Gentry, said in an interview Monday. “Kyle knew this guy just needed someone to be around him.”

Goldberg said one or both men likely had been drinking Saturday night. There was no indication of trouble between the two. Around 10:30 p.m., Hickman sent a text to his wife saying he needed to fix his tire, would do so the next morning, and planned to spend the night at Draa’s apartment, Goldberg said.

Exactly what made Hickman change his mind wasn’t clear. He was shot while working on the bike. “We believe that Kyle never knew what happened,” Goldberg said.

Officials will know more details about alcohol consumption in the case several weeks from now, when toxicology reports are completed by Maryland’s Office of the Chief Medical Examiner. The police chief said Draa apparently had shared his struggles with only a narrow band of people, and “no one anticipated that he would take another life.”

The two men had different backgrounds, but their friends described an equal commitment to helping students who had disabilities and learning difficulties.

Draa, who was engaged to be married, was from the Baltimore area, according to his Facebook page. He enrolled at the University of Maryland and, by 2004, was serving in the Marine Corps, according to his LinkedIn profile and a Marine spokeswoman. Draa was an infantry officer assigned to the 1st Marine Division, based in Camp Pendleton, Calif., and was deployed as part of Operation Iraqi Freedom from Jan. 22, 2006, to Aug. 17, 2006, according to the spokeswoman. He was a first lieutenant and earned a Combat Action Ribbon, among other awards.

Draa left the Marine Corps in July 2008, the same month he joined the San Diego Police Department as an officer, according to the Marines and his LinkedIn profile. A San Diego Police Department spokesman confirmed his service there.

He moved back to the Washington area, earned a master’s in special education from Maryland and by 2010 was working as a special education teacher in Maryland.

At some point during his teaching career, he met Hickman, who had grown up in Kansas and had gotten married two years ago.

“A gentle person,” said Gentry, his close friend. “He was someone who wanted to take care of kids with disabilities.”

Hickman enjoyed riding his bike and engaging with those around him. “Kyle could make a friend any time,” said Gentry.

In Draa, he met someone who seemed to share his dedication to special-needs kids. Draa worked with emotionally disturbed children and teenagers — “some of the most challenging students you can work with. It takes a calm demeanor to do that,” said Demond Moy, founder of Achieve Tutoring, an after-school math and literacy program where Draa also worked.

Draa often cycled to work wearing fatigue-patterned spandex, Moy said. At another school where he worked in the District, High Road Primary and Middle School, Draa was named staff member of the month in December.

Karen Rivas, another friend of Hickman’s, said he and his wife, Lindsey Crifasi, owned a home together in Northeast Washington. Rivas described them as “avid bikers and environmentalists and anti-violence kind of people.”

Magda Jean-Louis contributed to this report.