Your mate stole your diamonds and called it “borrowing.”
He’s now borrowing a cell.

Go To Jail brings handcuffs, tasers, police uniforms, and inmate clothing to Minecraft Bedrock. Arrest players and mobs, round up suspects, and give that prison you built an actual purpose.
Your prisoners can’t just mine their way out. Arrested players can’t mine or use tools, so the pickaxe you forgot to confiscate won’t be much help. The cuffs unlock with keys. Keeping track of those is probably a good idea before your friend spends the entire evening shouting through iron bars.
Haul cuffed mobs with leads. Personally escort that overpriced villager into custody. Twenty emeralds for something you found in a chest? He can explain that to the judge.
Bring a taser for escape attempts. Some people hear “stop resisting” and immediately start sprint-jumping. You have equipment for that.

Dress officers in police uniforms and prisoners in inmate clothing so everyone knows who’s supposed to be chasing whom. Whether the officer is actually the biggest criminal on the server is between you and your friends.
Build a prison, play cops and robbers, or finally investigate the guy who keeps blaming creepers while carrying your missing TNT.

Download Go To Jail. Your server already has suspects.