What other information do you have (if any)?

Did you find him in Census records?

Did you find a death certificate?
You MAY be able to use it to get additional info:
Parents: Will assist in finding him in the census records - and perhaps their death certificate. Also may help find other siblings (through census and marriage records).
Informant: May have been a relative or neighbor. The neighborhood could contain other relatives.
Cemeteries: He may have been buried with other family members.

Did you get his daughter's death record? Does it have any more information? Amelia was born ca 1860, and died in 1928 (St. Landry).

What about other 'Atemans'? You may have to trace them through census and marriage records. The surname is somewhat different, which will make it easier to research. However, the possible spellings may prove time consuming (also try Achman, Aikman, Agman, Acmain, Augman, Adman, etc.). Still, worth the effort.

A Ned Ateman also married in St. Landry (1875: Opelousas #8412).
A Mary Harris Ateman also died in St. Landry (1925).

In 1900 (Washington, LA), Valmont and Amelie Larose were living near (enumerated next to) Wash? Aitman (78) and wife Mary (48). Mary had four living children. This would imply that Wash/Watley? was born ca 1822. Could be related?

In 1880, Wash? and Mary ATMAN were living 'near' Valmon and Amelia. THIS time, Wash is listed as a 38 year old male - not much older than Amelia (30). There were three children in the household: Jimmy, Harrison, and Harriet - ranging in age from 13 to 7.

Sidenote: Also enumerated next to Valmont in 1900 was a Robert Shield and wife, Rachel. Living in the household was a 13 year old, 'Martha LaRose', Sister-in-Law.

I could not find Mary and "Wash" in 1870 ST. Landry, but I found a very interesting 'Watson YEATMAN', 46 year old, born in KY. Could this be yet another spelling for 'ATEMAN'. Remember, the 'Y' was mostly silent for people with a french accent.
He was living with Edmund Taylor, near Alfred Taylor. This is only noteworthy because Wash Atman was also living in a neighborhood with Taylors and Lees in 1880 and 1900.
Note also that KY was the reported birplace for the 'father' of Amelia Larose in the 1920 Census. Coincidence? Census Taker error? Perhaps.