Our family had a cousin who passed on in a mental hospital in NY in 1933. He was 24 years old. The cause of death cannot be interpreted today as anything meaningful, and I've asked doctors about it.
Have you found him on the 1880 census? Some of the 1880 census questions, if answered, may prove helpful, i.e.
Was, on the day of the enumerator's visit, the person was sick or disabled so as to be unable to attend to ordinary business or duties? If so, what was the sickness or disability?
Was the person blind?
Was the person deaf and dumb?
Was the person idiotic?
Was the person insane?
Was the person maimed, crippled, bedridden, or otherwise disabled?
Had the person attended school in the past year?
Can the person not read?
Can the person not write?
See the full list of column headings here:
You can search the 1880 census here:
And, the 1885 NJ State Census here:
You can search his name in old digitized newspapers: