Arbie LaBruckman was suspect of killing Carrie Brown initially, though how seriously, it is unknown. Could Arbie LaBruckman (Frenchy) have been LeGrand? I don't have the information of where LeGrand was in April, and I don't know who might, though I suspect Tom Wescott might know.
It's just somewhat coincidental (as are many things in the JTR world) that there was a victim with massive amounts of mutilation in Brown. She was a prostitute. Her lodging house or room for the night was also owned by a man of Irish Descent (Fitzgerald). There was a man with a foreign accent, nicknamed Frenchy that was at least in the general area and was considered to be a baaaad man like LeGrand. He also seems to have been in jail in 1889 in London, much like LeGrand, and his name is French and actually sounds totally made up.
There are several things wrong with your theory, I'm afraid, not the least of which is the fact that La Bruckman was able to provide an alibi for the night of the murder of Carrie Brown. This alibi, that he was at Tommy Bennett’s lodging house at No. 81 James Street, was fully corroborated by the people at the lodging house and the police dropped him as a suspect. He had nothing to do with Carrie Brown’s murder.
It should also be pointed out that there was enough information provided by La Bruckman himself, and people who knew him, to both track his movements and prove who he said he was: a 29 year old, originally from Morocco, who had moved to New York with his mother and sister in 1870, and who had become a cattleman on board cattle boats which operated between New York and London and who had done this since the age of 15. There is absolutely no evidence that he was arrested or in jail in London in 1889. He was not LeGrand
Brown’s body was mutilated but there were not “massive amounts” and the mutilation didn’t compare with that inflicted upon the Whitechapel victims. The man who owned the East River Hotel was not named Fitzgerald (he was merely the 21 year old night doorman and sometime assistant bartender) but James Jennings. The Lower East Side was filled with men with foreign accents and “Frenchy” was a common nickname because of this and the Water Street area around the hotel where Brown was murdered was considered one of the worst in the city and was filled with “baaaaad” men. None of this connects Charles LeGrand with Arbie LaBruckman.
I'm just now seeing this thread. I have to agree with Wolf that there's no relation here. However, one of Le Grand's popular nicknames was 'The French Colonel' and it is actually possible he was in America in April 1891.