Emmoni Thomas, who manages a Five Guys burger restaurant in the District’s NoMa area, was leaving work Tuesday afternoon when she saw a crowd of teenagers brawling in the street. Right away, she knew the melee was more than just fisticuffs.

“The young man collapsed to the ground,” Thomas, 19, said later, referring to a high school sophomore who, it turned out, had been stabbed.

It was a little past 4:30 p.m. on a busy stretch of Second Street NE, near Florida and New York avenues and the NoMa-Gallaudet Metro station.

“I ran over and tried to perform CPR,” Thomas recalled. But the 16-year-old victim, a gifted and diligent student named Tyshon Perry, who had tried to steer clear of trouble and looked forward to college, was bleeding from a wound on the heart side of his chest.

“It was too late,” Thomas said.

Within an hour, Tyshon, who aspired to a career in the FBI, was pronounced dead at MedStar Washington Hospital Center — one of 50 people and the sixth juvenile listed as homicide casualties in the city this year. The other young victims were a baby, a toddler and three teenagers, including a 14-year-old boy shot in an attempted robbery.

At week’s end, with the stabbing still under investigation, staff members at KIPP D.C. College Preparatory charter high school, several blocks from the crime scene, were mourning the loss of a dean’s list student they described as bright and mature.

They remembered a math whiz and intramural football player who was respectful of adults and easygoing with his classmates, bridging the eternal social gap between brainy and athletic cliques in school. “He was one of those students you go into teaching for,” said his faculty adviser, Mallory Loveridge, as she broke down in tears.

Meanwhile, five miles east of NoMa in a tidy duplex in the Deanwood neighborhood, the slain youth’s parents sat in the heavy stillness of their living room, speaking in low tones on a summerlike Friday as sunlight poured through a window.

They had finished making funeral arrangements for Tyshon, the second of five siblings ages 9 to 28. The church service is set for Saturday, Mother’s Day weekend.

“He was a great kid,” said his father, Shonpaul Perry, 46, who works as a driver for the D.C. public library system. “He was a people person. He was outgoing. He was well loved by many, many people. He was intelligent. Honor roll. He was not a problem as a kid. He was not in the street. He was not gang-banging. He wasn’t hanging out. He wasn’t bringing strange company into our home. No, sir.”

His mother, Gina Nixon-Perry, 38, said, “He’s been that way since he was little.” Nixon-Perry is employed as an aide at the city’s Parklands-Turner library, and Tyshon helped her there once a week, usually Sundays, as a volunteer.

Nixon-Perry said that as Tyshon was bleeding on the ground Tuesday, an unidentified teenager who knew him grabbed the wounded youth’s iPhone and said, “Siri, call Mom.” “Mom” was how Tyshon had listed his mother in the phone’s contacts directory. At the library, Nixon-Perry’s phone rang, and she answered.

“Tyshon got stabbed!” the caller yelled in a panicked voice, according to Nixon-Perry. The caller told her to hurry to the NoMa station, where Tyshon regularly boarded a subway train to Deanwood after school. “Tyshon’s dying!” the caller said.

As Nixon-Perry’s boss started driving her to NoMa, she called her husband. Then, her phone rang again. This time, someone from the KIPP school was on the other end, telling her Tyshon had been rushed to MedStar Washington Hospital Center. She and her boss diverted to the hospital, and so did Tyshon’s father.

When they got there, he was dead.

“We are heartbroken,” Susan Schaeffler, chief executive of the KIPP charter school network, wrote in a letter to parents last week.

Tyshon entered the KIPP system in 2011 as a fourth-grader at Key Academy, where teachers immediately noticed his advanced math skills. He later attended McKinley Technical High School in Northeast Washington. But he transferred last year to KIPP D.C. College Preparatory to start his sophomore year.

“He was a beloved member of the community,” said Tom Clark, a KIPP spokesman. “He was very outgoing and social. . . . Teachers loved working with him.”

Loveridge, his adviser, said Tyshon was exceptionally polite and almost always on time for his classes. Even with adults he didn’t know, he had a way of remaining playful yet respectful. Any task a teacher asked him to do, he did. He was lighthearted in social settings but serious about his schoolwork.

From an early age, his parents said, he talked about a career in the criminal justice field, and in recent years he was focused on federal law enforcement.

“He wanted to be the first black director of the FBI,” Nixon-Perry said. As for college, her husband said: “We hadn’t locked onto one particular university. But we had our eyes on the Ivy League. We were shooting for the stars.”

On Friday, Perry walked to a counter in his kitchen, picked up a blue binder and carried it to the living room. “If you don’t mind,” he said, holding out the file, “look at this.”

The folder is thick with Tyshon’s school achievement certificates, which his parents collected for more than a decade. The stack begins with a “Kindergarten Completion” certificate and ends with a dean’s list certificate from KIPP, awarded in March.

Page after page: “Honor Roll,” “Academic Excellence,” “Great Work,” “Outstanding Student,” “Congratulations,” “Music Perseverance,” “Big Dreams.”

Loveridge said Tyshon was popular among his 700 classmates. “He’s a kid who had such full potential,” she said. “He was the last person I thought this could happen to.”

Clark, the KIPP spokesman, said, “There never was any indication he would’ve been into any altercation or any sort of violent behavior.”

KIPP D.C. College Preparatory, on Brentwood Parkway NE, is about a mile from the NoMa subway station, and Clark said many students commute on Metro. The NoMa-Gallaudet stop is the closest to the school, which lets out about 4:15 p.m.

Tyshon was in a large group of teenagers who began arguing and then fighting near the station, according to police. Investigators said they weren’t sure whether Tyshon was targeted or was even involved in the altercation.

Thomas, the Five Guys manager, who graduated last year from the District’s Eastern High School, said the combatants were not much younger than she is. “I know somebody saw what happened,” she said. “There were too many people out there not to see something.”

Perry and his wife said they hadn’t visited the place where Tyshon was stabbed. But eventually they will, they said. And they will look for Thomas, who tried to save their son’s life — who tried CPR, but it was too late.

“I’m going to go and thank that manager at the Five Guys,” the grieving father said quietly. “Yeah, I have to go and thank her, tell her how much I appreciated it.”

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