Tyrone Lewis was a killer long before he was charged with shooting an Alexandria activist and tossing his body down a well, police said.

On Monday, Prince George’s County police accused him of fatally shooting a Prince George’s cab driver who was giving him a ride in 2005, and gunning down a basketball-loving teenager on the street in 2011.

The 26-year-old charged in connection with the slaying of activist Lenny Harris is now facing three separate murder cases — each apparently sparked by Lewis’s desire to rob someone, police said.

Homicide detectives were first tipped to Lewis’s suspected role in the earlier cases when they were probing Harris’s slaying. Associates of Lewis told detectives that their top suspect in Harris’s high-profile killing had told them of his involvement in earlier killings — ones that occurred long before Lewis shot the activist in the head and dumped his body down a well, police said.

Lewis knew Harris through his T-shirt business and set out with two other men to rob him because he mistakenly assumed the activist was rich, law enforcement sources have said. But in the other cases, Lewis targeted strangers, police said.

He did not know Edmund Akofio-Sowah, 45, a District Heights man who, according to family members, had four children in Africa and worked as a cab driver because he saw it as a type of entrepreneurship. Police said that he was giving Lewis a ride on Jan. 26, 2005, and that Lewis shot him during a robbery.

Nor did Lewis know 17-year-old Justin Isaacs, a teenager who, according to family members, loved playing basketball even though he stood no taller than 5-foot-6. Police said they think Lewis and another man gunned Isaacs down on Oct. 10, 2011, during a robbery on the street in front of Isaacs’s Hillcrest Heights home.

Family members of Akofio-Sowah and Isaacs said they were pleased — and shocked — to hear news of Lewis’s arrest.

“I couldn’t believe it,” said Ruth Akofio-Sowah, Edmund Akofio-Sowah’s widow. “I’m just glad that we can finally put some closure to this, and it’s justice after all.”

Patricia Isaacs, Justin Isaacs’s aunt, said, “Finding someone doesn’t bring him back, but at least we know that someone will hopefully be punished for the crime.”

Police and prosecutors still face a long legal road ahead. According to police charging documents, the case against Lewis in Isaacs’s slaying hinges largely on an unnamed witness who talked with Lewis about the slaying, and on the word of Kelvin Walker, 22, who is also charged with first-degree murder in the case. According to the charging documents, Walker “provided an oral statement confessing to his involvement” in the crime and “implicated” Lewis. He is jailed in a separate, home invasion-burglary case in Charles County, police said.

The case against Lewis in Akofio-Sowah’s slaying is also based in part on an unnamed friend of Lewis who told detectives that Lewis was responsible for the cab driver’s death, according to police charging documents. In that case, according to the documents, the friend identified the exact caliber of handgun that was used in the crime, and another cab driver picked Lewis out of a photo lineup as the man who robbed him about two weeks earlier at the same intersection where Akofio-Sowah was shot.

Felecia Lewis, 48, Tyrone Lewis’s mother, said her son was not involved in any murders and plans to fight the charges against him. She said her son only learned of Harris’s murder on the news, and the evidence in the two earlier cases was flimsy, based mostly on hearsay.

“They are trying to put charges on my son for no reason. Because somebody said something? Come on,” Lewis said. “Do they have any evidence on my son to say he did any of these things? No, because my son didn’t do any of these things.”

Lewis said her son worked at Target and a bakery before he was incarcerated on a separate, grand larceny charge in Fairfax — where he is currently being held. She said he was active at the Holy Mountain of God church in the District and enjoyed playing football.

“They’re portraying him to be a bad person when he’s not,” Felecia Lewis said. “My son is not no murderer. He’s a family person. He loves everybody.”

Family members of Isaacs and Akofio-Sowah said that while they did not know Lewis, they were hopeful he would be jailed for life if the allegations against him were true.

“He hasn’t learned,” Ruth Akofio-Sowah said, “so there’s no need for letting him back out.”

Staff researcher Jennifer Jenkins contributed to this report.