A column and a half news article in the Bangor Daily Wig and Courier from 19 Feb 1891 states that he was about 35 years old, 5' 8", stooped shouldered, wild black eyes, high cheek bones, thick lips, straight black hair, and speaks with a Lancashire brogue. Also speculates that he was of French/Indian heritage.
Yet another DeCourcey to add:
Sing Sing Prison Admission Register, February 1882
John DeCourcey, age 24
This man stated that he was born in Ireland and was a bricklayer; was Catholic and Single
Had gray eyes, bald, 5'9", 160 weight
Could read and write
Upon his arrest resided: 225 W 60th Street, NYC
Right after the address it looks like "Uncle Dennis DeCourcey" then it was written "Deputy Sheriff" and an address
In the description of John, he had several scars on his face, scowled badly, had lost "nearly all the hair off his head from disease" (could it have grown back later?), had full mouth and thick lips, his eyebrows were "straight and come together on the nose", his "head and face long and features large".
He had a large scar on the inside of his left arm near the shoulder, apparently from a burn. He had a blue anchor on his back and on the inside of his right forearm he had a small red cross.
Could one man have claimed that he was John DeCourcey, Oscar De Courcy, Thomas Howarth? Could he have told different stories about his life: he was born in England, New York, Canada, possibly of French/Indian heritage and now Ireland? Could he have changed his age at different times in his life? Was DeCourcy a name that was somewhat unusual, or was it a somewhat common name?
Update: If this was one man, he could have been on the move and could have learned how to mimic different accents, if need be. Or, he could have remained in one area for many years and could have picked up a slight accent.
Update, again. The above report appears to have been the one time that it could have had real facts, as Dennis appears to have been a Deputy Sheriff at the time (and one would think this would be the time to be honest). Dennis is in the 1884 New York Directory as dep. sheriff County C.H.