Can a thief use an iPhone 6s Plus that's locked-by-fingerprint?

[iMore Question]

My iPhone 6s plus got robbed some days ago. Right after the rob, I called my number and it was turned off. After that, I called again and I heard the ring. And then I was informed by Gmail that my Google account had a password change so did my icloud's password within 2 hours. Does it mean that the bad guy could unlock the 6-number passcode or the fingerprint lock? I just thought those were high secure

 

[iOS Gravity]

They shouldn't be able to. And since you said they turned it off, it removes the option to use Touch ID. If you have iCloud on it then you can remotely wipe the phone or track it. I'd recommend changing your passwords if it's not you making the changes.