Can they get into the phone if they know the passcode when it's in lost mode?

I had an iPhone with a passcode and it and it got stolen by someone I know. But they know the passcode to get in the phone. If the phone is in lost mode, can they still open the phone with the passcode? Or you you have to disable it through Find my IPhone? I won't report this person but I want to make sure they can't use the phone, even if they have it.

Damn I'm sorry but yes they can. When I'm angry I put my sisters phone on lost mode and all it asks her for is her password to take it off lost mode!

You can call your cell service, and deactivate the phone.

Tbtbtb