I'm studying John's brother, James Hagan. Both John and James Hagan were stone cutters who worked in Lafayette Cemetery No. 1 and 2. (James' old marble yard is now the "Rink" across the street from the cemetery) I mostly have newspaper articles concerning him as well as his son, and a few notarial archive documents. I can send you scans of them if you like.
Also, I'm sure you're aware - John Hagan and Jane Murphy are buried in Cypress Grove cemetery at the end of Canal street in New Orleans.
I'm curious how you know who his parents were. Did he and James have any other siblings? Also, that he met Jane Murphy in New York is interesting to me. If James and John were in New York before they arrived in New Orleans, I'd be curious to learn about it.
My e-mail is EAnneFord[at]gmail[dot]com. Feel free to contact me and I can send you those scans.