Purchase Proof/ Need Information On Account

Our condolences on your lost, we're here to help with options for the activation lock @yecrtv.

As mentioned by @formerlyknownas, if the device was purchased at the store, return to that location to request the proof of purchase. 

In addition, if you able to access the home page of the device, you can turn Find My off. From your Home screen:

If you’re returning, selling, or giving away your device, you must turn off Activation Lock. You’ll have to erase all content and settings from your device before handing it over. Keep in mind, erasing this will completely erase your device, turn off Find My, and remove the device from your Apple ID account.

To erase all content and settings, from your Home screen:

1. Tap Settings, then tap General.
2. Tap Reset, and finally tap Erase All Content and Settings.

If the above does not help and the device was purchased online, let us know and we'll meet in a DM to review purchase proof. Thank you for contacting AT&T Community Forums. 

Alasani, AT&T Community Specialist 

If he was on your account, you can call at&t and ask for that, or go to the physical store where it was purchased. 

If it wasn't your account, you may have a difficult time.