It's mentioned by Stella that Bert and Chad are wanted for murder in two other states.
Lone Ranger: (knocks poison out of Jeff's hand) Now put up your hands! No, doctor, you're not going to pay for your crimes by taking poison. If anybody takes your life, it'll be the law.
Jeff: (to Bert and Chad) You know Stella. She could get information out of a rock.
Cleve: I don't get it. Why the mask?
Lone Ranger: I have my reasons. I hope you'll trust me in spite of it.
Cleve: I'd be a fool not to after you saved my life.