Originally Posted by
rage2
His fingerprint wont work if the phone has been rebooted or if it's been ~24 hours since the last unlock. The lightning port also deactivates so external intrusion tools won't work unless it's unlocked. As others have mentioned, you won't be able to add your fingerprint or change password without his lock code. These are some of the newer security measures introduced by Apple to stop people from getting into other people's phones.
Now, what else can you do. Assuming he has iCloud backup and you know his Apple ID/password, you can simply let it charge, ensure it's connected to wifi (ie at home) and let it sit for a day to ensure the backup has kicked in. Then use his phone (or another phone) to restore the backup and you'll have access to everything on the phone, with your own lockcode, fingerprints, faceID etc set during the restore process. Those don't go to the backup as it's all stored locally in the secure enclave.
If you don't have access to his Apple ID but have access to his email, you can use that to reset his Apple ID credentials assuming you know his security questions.
Good luck, sorry for your loss.