When Isaiah Trotman visited his family in Ohio this Christmas, his mother said she noticed her 31-year-old son seemed unusually subdued. Fearing the change in his demeanor might indicate deeper problems, she said, she pleaded with him to move out of Washington, D.C., to be near her.

"I saw a depression," Althea Trotman said Thursday, a day after her son, an Auburn University graduate with a career in IT was charged with targeting commuters and killing a rail worker in a shooting at the Potomac Avenue Metro station in Southeast Washington. "I knew it was real."

Police said Thursday they were working to determine the motive behind the chilling, daylight attack, which renewed safety concerns on D.C.'s public transit systems and in the neighborhood east of Capitol Hill where it occurred.

Three people were shot, including 64-year-old Robert Cunningham, a Metro mechanic who police said was killed while heroically trying to stop the gunman. The two others were shot in the legs and wounded, and police said a fourth person hurt a hand while rushing away from the shooting.

A witness reported the gunman saying, "I'm the killmonger" as he entered the station in the 1400 block of Potomac Ave SE shooting.

Isaiah Trotman was being held Thursday in a hospital for mental health evaluation, according to D.C. police, awaiting arraignment on charges of first-degree murder while armed, kidnapping while armed and assault with a dangerous weapon. It was not immediately clear how soon he could appear in court.

In interviews, Trotman's mother and his ex-girlfriend said Trotman - who purchased a home in the Fort Dupont Park area in 2019 for more than a half-million dollars - struggled with depression, and they described events that may have contributed to his downward spiral, including the death of his father and the breakup that ended a sometimes-volatile relationship. His ex-girlfriend claimed he was abusive, and police were called to their home at least four times, by one person or the other, records showed.

Trotman also had imminent legal woes: Soon after his holiday visit, he pleaded guilty to possession with intent to distribute methamphetamine, and he was facing possible prison time at an April sentencing.

Althea Trotman, learning about her son's arrest for the first time Thursday, broke down in tears. "It hurts so bad," she said during a lengthy telephone interview, noting her son had once been fit enough to serve in the Air National Guard. "It's not fair. Isaiah worked so hard."

Police said the shootings began Wednesday when Isaiah Trotman followed a passenger off a Metrobus and shot that person in the legs. He then went down the escalator and shot another person in the leg at a Metro fare-card stand, police said.

In the Potomac Avenue Metro station, Isaiah Trotman approached a woman on the platform while holding a gun at his side, police said. Cunningham tried to intervene, police said, and he was fatally shot. A second transit worker tried to de-escalate the situation, and other riders on the platform tackled the gunman before police took him into custody, authorities said.

Trotman's mother said she grew more worried in recent weeks when her son stopped returning her calls. Around the same time, his counselor called D.C. police and told them he had stopped showing up for sessions, asking that officers be sent to Trotman's home on Jan. 19 to check on him, according to an incident report.

Police said they checked the outside of the house and knocked but did not make contact with him. In the report, police said they left after finding nothing "out of the ordinary or unusual." Efforts to reach the counselor were not immediately successful Thursday.

Trotman was also facing prison time in Adams County in Pennsylvania, having pleaded guilty Jan. 12 to possession with intent to distribute methamphetamine, according to District Attorney Brian Sinnett. He said Trotman was arrested nine months ago in a motel lobby, where he was seen acting erratically and vandalizing plants. His sentencing is scheduled for April.

The youngest of three children born in Nashville, Trotman lived most of his young life outside of Atlanta, his mother said. He was regarded as the studious one. His mother said she left him as a teenager with friends to tend to a sick relative in Alabama; she said they were surprised that he refused to go out and play basketball until he had completed his homework.

He took to competitive swimming, his mother said, and moved in with his aunt in Alabama to attend a prestigious high school for his senior year. She said he got a scholarship to Auburn.

The university said in a statement that Trotman had worked in the school library and graduated in 2015 with a BSBA degree in finance. His mother said he joined a military program while in college. An Air Force spokesman said he had been with the Air National Guard; the guard did not respond by late Thursday afternoon.

Work took Trotman to various cities, including Charlottesville, where he met Allegra Cooper, now 29, around seven years ago, Cooper said. She said they planned to marry, and he bought a house for them in D.C., where he was working.

The light-gray, seven-room brick house sits atop a hill on a quiet, tree-lined street with landscaped yards and tall trees. D.C. records showed all tax bills to date have been paid.

Cooper described her relationship with Trotman as fraught. She said that he was controlling and that he would scream at the smallest of issues, such as which lane of traffic she was in. She also said he dressed in suits, had two vehicles and kept his house clean and tidy, and worked in information technology.

D.C. police responded to Trotman's house four times in 2019 and 2020 for domestic trouble, according to reports. Police said that Trotman was arrested at least once but that charges were not pursued. Once, Cooper told police he ripped up her money and tossed it on the street. Another time, Trotman called police during an argument that did not become physical, a report said.

In June 2019, court records show Trotman obtained a temporary protective order alleging that Cooper refused to leave his home and threatened him, "saying she'll find a way or someone to pay me back." A week later, records showed, Cooper called police for help retrieving property from the home, and another argument ensued over the items.

In August 2020, police said an officer in the 1200 block of U Street saw Trotman swing at a group of women, cutting one on the lip. He was arrested and charged with simple assault, though there was no record the case was pursued in court.

Cooper said she left Trotman about two years ago and moved back to Charlottesville. About six months ago, she said, he showed up at her home and broke the front door to her residence. She said she called police but did not file charges.

She said she was in D.C. about two months ago and stopped by the Fort Dupont house. She said the inside appeared disheveled with graffiti on the walls, unlike the way he had kept it when they were together. Cooper said he didn't have a phone or a car, and she didn't know if he was still working.

"I saw the decline," Cooper said. She noted that the breakup had been hard on him. "He thought I'd never leave," she said.

Althea Trotman, a retired medical technician, blamed Cooper for the frayed relationship with her son. She said there was also family tension after her ex-husband died and her son attended the funeral against her wishes. Her ex-husband, she said, had not been involved in their son's life as a child.

"He would always be talking positive, but I knew he felt sad," Althea Trotman said.

Althea Trotman said she drove her son back to D.C. after the Christmas break in Columbus and stayed at his house for a few days. She said she saw no graffiti on the walls, as Cooper had alleged.

Though Isaiah Trotman had not picked up when she called in recent weeks, his mother said he did answer when his brother called this past Friday. She said she listened in on the call but did not let him know she was there. She said he sounded fine, even "kind of happy."

Days later, a reporter told her of the allegations against her son. She was outside a store, she said, and she "went in and couldn't stop crying."

Of her son, she sobbed: "He was the good one."

The Washington Post's Katie Shepherd and Keith L. Alexander contributed to this report.