The four accused were charged with aggravated assault following an altercation with another inmate at a correctional centre.
The incident began as a consensual fight between one accused and the victim, but moved behind a partition out of view of surveillance cameras, where the victim sustained severe, life-threatening head injuries.
The Crown relied on surveillance video and the testimony of another inmate, but did not call the victim or other eyewitnesses.
The court found the inmate witness unreliable and the video insufficient to identify two of the accused.
Furthermore, the Crown failed to prove who inflicted the injuries or that there was a common intention to assault the victim.
All four accused were found not guilty.