Due Process

I would like to inquire about the harassment case that was charged to my friend because he was automatically put under preventive suspension without investigation.

The main office called him and showed him the letter made by the complainant. He was given a chance to explain in writing but  was not even given enough time to respond. They just asked him to explain right away After a few hours or less, they made a decision to suspend him without conducting an investigation. No evidence or witness was asked. They just based it on "she said" thing.
That time, my friend was shocked so he just agreed on what they want.

When he went home, I  asked him for a copy of the letter of complaint and the notice of his suspension and he said that he was not provided any copy or documentation.  He denied the allegation so I believe he should still be given due process.

And I'm also questioning the HR people because cases like this should be confidential but it seems that everyone in their office knows what happened. Even those who ae working on a different branch is texting him about what happened.

Can we file a complaint against  the company for not giving him the due process? What about the confidentiality issue?
The complainant t is also texting my friend that he can be jailed for what he did. That her fiance is from the army and his uncle is a police officer.  My friend already lose his job eventhough its just a suspension, because he don't want to work there again due to the disgrace he got for what happened even if he was not given the due process.

And let's say he will be proven not guilty, what charges can we file against the complainant?

He can file for Illegal suspension

What about confidentiality?

u said earlier that your friend was put under preventive suspension, then suspension at the end. remember that preventive suspension is completely different from suspension.