[bluesaunders]

In that case, they could just bring the phone down to the morgue and unlock it with touch id.

[katbyte]

Touch ID does not work after a reboot, to many attempts or a long of delay.

Additionally you don't have to use your thumb, so if you don't know what body part was used your out of luck.

[lololomg]

If the phone is rebooted or if 48 hours have passed since the last passcode was entered, the touch ID can't be used to unlock the phone.

[mef]

Touch ID requires the passcode after reboot or timeout. They'd need to do it very quickly.