The video that shows the violent incident and students laughing at a Georgia school has been viewed more than 5 million times on Twitter.
The 12-year-old Atlanta boy has been removed from the home after his mother shared the video on Instagram Live.
Police and prosecutors suspect her death was a hate crime.
Danny Henson was shot to death in Baltimore, Sophie Vásquez in Georgia.
The DOJ filed a statement of interest in Ashley Diamond's case against the Georgia prison system, which she says failed to protect her from sexual assault and denied her health care.