Towanda Kellam said the threats and intimidation of her 15-year-old son Lance Hartgrove started on Facebook several months ago.

Soon afterward, he was being chased home from school. The perpetrators cornered him in late February, knocking out his front teeth, she said. On Tuesday, Hartgrove was heading home after playing basketball, riding his bike near 10 Malcolm X Boulevard when he was stabbed to death.

“These same little punks said they were going to kill my son,” she said as she struggled to keep herself calm Wednesday. “My son was 15 years old. That was my baby. My son wasn’t a robber. He wasn’t a killer. He wasn’t a drug dealer. He didn’t have a criminal record.”

Advertisement - Continue Reading Below

Boston police said the attack behind the Social Security Administration office in Roxbury ended with three people stabbed, two of whom survived. Police have not released the name of the dead victim, but Kellam said it was her son.

An uncle of the victim, Donald Kellam, tears flowing down his face as he stood with the boy’s mother, held a picture of his slain nephew and said the threats over Facebook were clear.

“They said they were going to brush him,” he said. “That means they were going to kill him.”

Kellam said that she is not certain why her son became the focus of the violence, but said that in February her son was chased home from school, and she stepped in to thwart any violence.

“They tried to hurt my son, but I was home, and I wasn’t going to let that happen,” she said.

But 10 days later, her son could not escape, and he was hit in the mouth, an attack that knocked out his front teeth and required surgery to repair, she said. He was attacked again May 30, hit in the mouth with a heavy object.

“They saw my son again with his friends, and they hit him in the mouth with an object. What kind of object, I don’t know, but they fractured his teeth all over again,” she said.

Kellam said her son was being threatened by people who claimed a connection to Wheatland Avenue in Dorchester.

Kellam said that her son started skipping school to avoid confrontation with the people who had targeted him for violence and that she sought ways to keep him safe and in school, even contemplating a Probation Department monitoring bracelet to help her keep track of him.

The stabbings took place at around 1 p.m. in the busy heart of Roxbury. The area is home to a mail handling facility, the MBTA’s Dudley Station, and the John D. O’Bryant School of Math and Science.

Also in the neighborhood was a Hollywood film crew making a buddy cop movie starring Sandra Bullock and Melissa McCarthy, called “The Heat.”

Police and Suffolk District Attorney Daniel F. Conley’s office continue to investigate the fatal stabbing.

Hartgrove’s family held a vigil at 6 p.m. Wednesday on Malcolm X Boulevard near where he was stabbed to death.