The men accused of robbing and killing Lenny Harris knew him the way most people did — as an outspoken community activist and T-shirt salesman. Detectives think they assumed, mistakenly, that he was rich.

The men arranged to meet with Harris one night in September, according to law enforcement sources, but authorities say it was a set-up for a robbery. Investigators think Harris was forced into a stolen van, bound with duct tape and driven to a vacant, isolated property in Fort Washington, the sources said. There, he was shot and dumped into a 20-foot well.

On Monday — a day when hundreds of people gathered at a D.C. church to mourn Harris’s death — police announced that they had obtained a warrant charging Tyrone Lewis, 26, with murder, alleging that he shot Harris. Police had already charged two other men — Linwood Johnson, 49, and Ivan Newman, 20 — in connection with Harris’s death. Police said their search for those involved in the killing is over.

The mystery of Harris’s disappearance vexed detectives in two states for months — and captured the D.C. region’s attention. Detectives now think the crime was as simple as it was senseless: a thuggish crew allegedly set out to rob a man who would probably have given them what little he had.

“Robbery is clearly the motive,” said Maj. Michael Straughan, who commands the criminal investigations division for the Prince George’s County police department. “He’s a public figure. He’s known in the community.”

Deborah Harris, 56, the wife of the Alexandria activist, said her husband had little to take and that the family was facing foreclosure from their Del Ray home.

“It’s surreal,” she said. “These people don’t really know who they hurt.”

Deborah Harris said that Sept. 21 began like any other day for her husband: He had oatmeal for breakfast and gave her a kiss as he walked out the door. About 4 p.m., she said he called to complain that he was tired and was going to go exercise.

Tony Suggs, a longtime friend, said he saw the activist even later, when the two talked at the Charles Houston Recreation Center in Alexandria. Suggs said he did not initially notice anything unusual about the way Harris, 53, was acting, but when detectives talked to him about his friend’s cellphone use that evening, it struck him that Harris seemed to check his phone frequently.

Investigators think sometime after that, Harris met with Lewis, Newman and Johnson; cellphone records show Lewis called Harris that night, law enforcement sources said. Exactly why they got together remains unclear, but Harris and Lewis had met sometime before through his T-shirt business, a law enforcement source said.

That source and the others in this article spoke on the condition of anonymity because the investigation is ongoing and they could be disciplined for speaking publicly about the case.

Deborah Harris said her husband worked mainly at his pest control business, although he had started the T-shirt company, Mycha, to teach his 20-year-old daughter, Myia Charde Harris, about entre­pre­neur­ship. The company name, Deborah Harris said, stands for “my child,” and Lenny Harris formed it using the first letters of his daughter’s first and middle name.

Deborah Harris said that if the men set out to rob her husband, “they were disappointed in that, because he didn’t have money.” She said he was investing more cash into his T-shirt company and pest control business than he was making.

What little he did have, Deborah Harris said, he usually spent on an annual community festival. “He really was a wonderful, giving, kind person who really loved God and his community,” she said.

The assailants took the activist’s bank card and possibly some other items, according to police charging documents. Police think he was killed soon after his disappearance.

Lewis, Newman and Johnson all have criminal records — although Lewis’s appears to be the most serious. He pleaded guilty in 2006 in three robbery and weapons cases and was sentenced to five years in prison. Then, in October, he was charged with violating his probation in those cases when Anne Arundel County police arrested him in a drug and theft case, court records show. He was indicted the same month in a grand larceny case in Fairfax County, where he is being held, police said.

Straughan said Lewis has ties to the area where Harris’s body was found. Authorities also say Lewis is the tattooed man caught on an ATM surveillance camera using Harris’s bank card

Efforts to reach family members of Lewis, Newman and Johnson have been unsuccessful.

Hundreds of Harris’s friends and family members filled Greater Mount Calvary Holy Church in Northeast Washington on Monday for a memorial service. Deborah Harris and her daughter, both wearing dark sunglasses, sat with their arms around each other in the front row, occasionally wiping away tears that ran down their cheeks. There was no casket to carry his remains.

The service celebrated his life. People swayed and sang as images of the activist were beamed onto giant projector screens at the front of the church. Alexandria Mayor William D. Euille drew laughs from the crowd as he joked about the times he and Harris disagreed on political issues. Bishop T. Cedric Brown said Harris had lived a full and productive life before he died, and he challenged those gathered to do the same.

“Lenny was ready for his appointment, as tragic as it was,” Brown said. “The question is, will you be ready when it’s your turn?”