Lennon Lacy, 17, was found hanging from a swing set by two belts in Bladenboro, southeast of Charlotte, in August.

It was confirmed on Friday that a federal agent has been assigned to investigate the case.

Rev. William Barber, the president of the North Carolina National Association for the Advancement of Colored People (NAACP), which was invited by the Lacy family to carry out its own investigation, said there were many unresolved questions that needed to be addressed.

Four days after Lennon's death, local police said there was no sign of foul play and his death was ruled a suicide by the state medical examiner.

According to his mother, Lennon had showed no sign of suicidal thoughts or depression.

“I don’t have a reason why the death of my 17-year-old boy still has so many questions,” said Claudia Lacy. “Why wasn’t it taken seriously?”

His family and the NAACP called the death suspicious for months, especially after Lacy's grave was desecrated only a few days after his burial.

The authorities later raised doubts about the initial findings and launched the investigation into the case.

Several hundred people demonstrated through the town on Saturday to call for a fresh investigation into Lennon’s death.

The demonstrators said they believe the case was another example of police mistreatment of African-Americans.

The United States has been the scene of protests against police brutality after grand juries in New York City and Ferguson decided not to indict white police officers who killed two black men.