Question

found him guilty of murder.
change in passive voice

Answer 1

Active: We found him guilty of murder.

Passive: He was found guilty of murder (by us).

The articles written in the bracket are not necessarily added to the passive structure of the sentence.

Answer 2

$\huge \textbf{ HEY \:MATE}$

He was found guilty of murder is the correct passive voice of the sentence.

$\huge \mathcal { I \: Hope \: It \: Helps }$