Isaiah Harris, 15, and his best friend walked along the 1400 block of New Jersey Avenue NW on Monday night. It was late, about 10, and Isaiah should have stayed home on the orders of his mother, Geneva Harris.

“But he was just being a hardheaded kid,” said his father, Raymond Carter. Isaiah went out to visit a girl in the neighborhood.

Police say a man named Eugene Kelly, 26, rode by on a bicycle and spotted the two boys. He slowed down, according to a witness. Kelly told the witness his brother had been killed, and it was time to get revenge.

“Someone’s gonna pay; I’m gonna go get my gun,” he told the witness, according to a police affidavit filed in court.

Gunfire hit Isaiah’s friend, a 14-year-old middle school student, in the leg, and Isaiah was hit in the buttocks. Isaiah died 43 minutes after he arrived at Howard University Hospital.

On Thursday night, teen boys wearing white tank tops and shorts convulsed and cried alongside family members, friends and school officials during a grief-stricken candlelight vigil that drew more than 100 people to the steps of Shaw at Garnet-Patterson Middle School.

Several speakers said that Isaiah took advanced math, visited museums and libraries with his mentor in the Big Brother program, and had two involved parents who came to every school meeting. He was the standout, the example, the boy growing into a young man who was on the right path.

“He got killed for the wrong reason,” said Isaiah’s best friend, the 14-year-old boy wounded in the shooting. The Washington Post generally does not name crime witnesses, and his identity was not released by police.

When Isaiah was born in March 1996, his parents had some troubles in their relationship, Carter said. But they were committed to raising Isaiah Harris together.

As he became a teenager, his mother worried about keeping him safe in their Northwest neighborhood and how to expose him to better role models. She signed him up, along with Isaiah’s younger brother Xavier, 10, for a local Big Brothers program.

He was matched with Jonathan Rothwell, who moved to the District in 2009 to work as a senior research analyst at the Brookings Institution.

In their first meeting last year, Rothwell, 30, took Isaiah bowling. Then they played basketball with Rothwell’s friends and checked out books at the Martin Luther King Jr. library. When they visited an exhibit about U.S. presidents at the National Museum of American History, they passed by uniforms, office seals and other objects used by presidents; Isaiah was especially excited to see President Obama represented.

“It gave him the sense that it’s not so unattainable to succeed and do something great in this country,” Rothwell said.

Rothwell told the mourners Thursday that Isaiah was equally at ease with his school friends and among Rothwell’s friends. “I could take him to a brunch party, and he would fit right in,” Rothwell said.

Police charged Kelly with first-degree murder while armed. He remains in jail.

Principal Kimberly Douglas said Isaiah was one of two eighth-grade students who took advanced math that is not offered at the school. So each day, he walked up to nearby Cardozo High School for his classes. “He was very mature,” Douglas said.

The vigil was the idea of several eighth-grade teachers, who felt that the students and staff needed a way to grieve for Isaiah while also honoring his life. At the school’s graduation ceremony next week, students plan to pin small ribbons to their chests and there will be an empty seat marking the place where he should have been with his classmates, Douglas said.

“I just signed his promotion certificate today,” Douglas said Thursday night, the document that marks his successful completion of middle school. Douglas said Isaiah’s family plans to attend the graduation, and she will present the certificate to them.