Police say three of the five teenage boys involved in a brutal attack of another student on a school bus have turned themselves in.

The attack took place during the afternoon of April 29 on a bus operated by Parkway Academy in Dover, Delaware. The incident was captured on video and quickly went viral after the victim’s uncle posted it online. The video shows the students repeatedly punching the victim in the back of the head.

After watching the video, police determined that the attackers attended Parkway Academy in Dover, Delaware, a school for at-risk students. They also say that the attackers are between the ages of 15 and 17.

On Friday, police announced that three of the suspects surrendered. Investigators say it’s too early to determine if bullying was involved.

“We don’t know all the circumstances as far as why it happened,” said Dover Police Corporal Mark Hoffman. “At this point, we’re just deeming it as an assault.”

Investigators say the bus driver did not stop right away when the assault took place. She did eventually report the incident to her supervisor however. Officials with Parkway Academy say that driver is currently on administrative leave as they work to determine whether she handled the situation properly. School officials also say they are working closely with police in the investigation.

While the victim is doing “okay” physically, the boy’s mother told NBC10 that the family is not ready to talk about the incident publicly. She also says the family has hired an attorney.