A Rapid City teenager who spends time volunteering at the Rapid City YMCA and whose mother calls him "a really helpful kid" is paralyzed after being thrown violently to the ground during an incident while walking home from school Wednesday.

Cody Yellow Thunder, 17, a junior at Rapid City Central High School, was walking near Rushmore Plaza Civic Center on Wednesday when an unidentified boy, also a juvenile, wrapped his arms around Cody's head and threw him to the ground, according to Cody's mother, Michelle Little.

The injured teen is in critical condition at Rapid City Regional Hospital.

Little said her son loves school and loves volunteering.

"He's really a helpful kid and helps out at the YMCA," she said.

She also said she is concerned that an arrest has not been made. Officials at the Rapid City Police Department said they are trying to sort out the details of the incident.

Lt. Dave Walton of the Rapid City Police Department criminal investigation division said the investigation in ongoing.

"We're trying to make a determination if we have a criminal violation," he said.

Walton said there were several witnesses to the skirmish, but all left the scene before police arrived. He added that investigators believe a cell-phone video may have been shot of the altercation.

"We hope someone will step up with the video. We would like to take a look at that," Walton said. "We're not looking to arrest anyone who was a witness. We want to see the video."

In an attempt to find the video, investigators have already searched thousands of videos on the popular video Web site YouTube but have not found the video.

Little said the incident happened shortly before 4 p.m. Wednesday, and officials called her to say Cody would be transported to Rapid City Regional Hospital. Cody underwent surgery on Wednesday and Thursday nights to repair some of the damage.

"I went to the hospital, and they said a surgeon would be right in. He told me, 'Your son is paralyzed.' I still don't think I believe it. I'm still praying he will be OK," Little said.