Question

the accused was found guilty of Murder change the active voice

Answer 1

They found the accused guilty of murder.

Answer 2

The court/ the magistrate/ the police found the accused guilty of murder.

An active voice goes in a sentence where the agent and not the object is given more preference.

For instance, in the court/ the magistrate/ the police found the accused guilty, it implies how the agent/ doer is doing the work that is in the predicate part.  

In passive voice, however, the stress will be on the work done, that is, on the action, and not on the agent.