Y heads.
Let me show you where to start.
The Death Master File. [DMF]
DMF is a computer database file made available by the United States Social Security Administration since 1980. It is known commercially as the Social Security Death Index (SSDI). The file contains information about persons who had Social Security numbers and whose deaths were reported to the Social Security Administration from 1962 to the present.
You can request data here: https://www.ssa.gov/dataexchange/request_dmf.html
Can government departments request information from the DMF or investigate the file?
No.
See how it was done?
At one point in time, Chicago was the wealthiest city in the world.