Two boys, ages 13 and 14, were taken into custody on Saturday.
The arrests came after their parents went to police complaining about harassing phone calls the teens were getting.
Instead, investigators turned the tables and took the pair into custody.
They were released to the custody of their parents on $2,500 bond.
Another 14-year-old boy was arrested on Monday night.
Action News reported David Henry encountered one of the suspects at police headquarters. When asked if he had anything to say about the incident, the teen said to his mother, "Am I going to have to beat him too?"
An apparent admission of guilt from one of the alleged perpetrators.
Police say more arrests are expected.
"We've received a number of telephone calls, 911 calls as well as calls to officers people know," said Tracey Duffy, New Castle County Police.
The video, which went viral after it was posted on social media, shows a 26-year-old Newark, Delaware man being beaten by several teenagers.
Click to watch raw video of the attack
Yana, who didn't want to give her last name, is the victim's mother. She described what went through her mind when she first saw the video.
"Rage, anger - because of the situation, with him being mentally disabled, he doesn't do anything to anyone but be kind," she said.
She could barely watch the video as a teenage boy body slammed her defenseless son, Karon, and punched him in the face - all as others watched.
Perhaps worse, there are other videos posted online showing other attacks on Karon, possibly by the same suspects.
Yana says Karon is living with Williams Syndrome and has the mental capacity of a second grader.
It's believed that one of the taped beatings happened sometime within the past week inside Harbor Club Apartments.
16-year-old Angeliz Marrero, of New Castle County, spotted the hard to watch videos.
"I was so mad, but at the same time, the first thing I thought was, 'I have to do something about this,'" said Marrero.
Armed only with her iPhone, Angeliz re-posted the attacks Saturday using #TheBullyProject.
Her Instagram followers went from 2,000 to nearly 20,000 in less than 24 hours.
"It spread so fast and I'm just so grateful for everybody that's helping me out because if it weren't for everybody helping, supporting and everything, this wouldn't even go viral and that man really deserves justice," said Angeliz.
Angeliz says she plans to continue using social media to bring awareness about bullying.
As for the victim, Karon's mother took him to AI DuPont Hospital for questioning in a medical setting to learn exactly when the incidents happened.
What does she want to happen from here?
"Just make people more aware that we need to be humane to one another," said Yana.
Anyone with information is urged to contact New Castle County Police at 302-573-2800 or online at www.nccpd.com.