I am flying blind on this. I have his bank statements so I know his income sources, but that's all I have besides his death certificate.
You're going to need help unless you have been appointed personal rep by a probate court or have possession of your friend's property.
First, you will need to file Form 56, Notice of Fiduciary Relationship with the IRS to let them know you are acting on behalf of the taxpayer.
What to file for a deceased taxpayer
If you are trying to obtain prior year tax information, please see the link below for more details from the IRS and how to request additional information.
Getting information from the IRS for a deceased person
Please see the following link for how to contact the IRS on behalf of someone else.
Contacting the IRS on behalf of someone else
You can complete the tax return for him. But be sure you have contacted the Social Security administration per the instructions in the link below before filing his return.
Assistance with filing a return for someone who has passed away
No, first, you need professional advice @richardrelliott1. If you are named executor in the will you could be held personally liable for any malfeasance. Contact a lawyer and tax pro.