GARDNER, Kan. -- Four classmates witnessed a beating that left a 16-year-old boy dead, and one of them recorded the incident on his cell phone, authorities said.

Investigators confiscated the cell phone as evidence, police said.

Dakota DeRemus, a sophomore at Gardner Edgerton High School, suffered from a heart condition and died after he was involved in a fight with another 16-year-old boy on Monday.

Juvenile authorities charged that 16-year-old with involuntary manslaughter in connection with DeRemus' death.

He appeared in juvenile court in Johnson County on Wednesday.

His mother cried through the proceedings.

DeRemus' father yelled out in court that the boy had bullied his son for two years, and officers in the courtroom slammed the father against a courtroom wall -- damaging it -- and cuffed him.

Immediately after the proceeding, both families declined to comment, but later, DeRemus' family issued a statement.

They then spoke out on Thursday, expressing their anger and grief.

DeRemus' grandmother, Rosella Davis, read from a written statement.

"If this rumor is true that they decided to videotape my grandson's death, then that is a sick thing to happen," Davis said.

Police said they had identified the four witnesses and were discussing the matter with the Johnson County district attorney's office, and additional charges could be filed in the case.

The process wasn't working quickly enough for DeRemus' father.

"You're no more than a murderer yourself when you're a witness to something like that and you let somebody die because you're afraid you'll get in a little bit of trouble and get grounded. I think it's sick. I will miss Dakota for the rest of my life. I hurt for my boy. I hurt for my family. We were very, very close, and I now I have an empty spot in my life that will never be filled," said Scott DeRemus.

A visitation was scheduled for Friday.

DeRemus' school was reviewing its harassment policy.