How to catch grifers on minecraft?

My friend has gotten a server recently. And someone has beem stealing from and destroying houses. He doesnt have that much staff. And im the head cop/dectective. So ive been trying to make plans to catch them. Nobody knows im a cop yet im working under cover. Ive only come up with one plan… Msg people and ask if they want to grief a house with me.

Read more: How to catch grifers on minecraft?