iCloud: Activation Lock - http://support.apple.com/kb/HT201365 - This is a security feature to deter re-selling of stolen devices.
Turn off Find My iPhone Activation Lock (formerly: Activation Lock: Removing a device from a previous owner’s account) - https://support.apple.com/HT201441 - If an activation lock was put on a device, only the owner of the account that applied the lock can remove it.
I have seen it reported if you take the phone, your ID, a death certificate, and probably the original sales receipt to an Apple Store they may be able to reset it for you, but that would result in loss of all content I believe. Unfortunately people have not yet grasped the concept of digital legacy.