I located a Horace Milton Nash listed on the Worcester County, MA census dated June 1, 1900. For a time frame when he was in jail, if you take nine months either way (prior to and after the June date) that may give you a starting point as to when he was there. Ref: Sheet 3, Enumeration Dist. 1823 on the census. Perhaps your contacts would be willing to look up his information for you now.
A Directory of Deceased American Physicians listed his death date as December 24, 1905. Do you already have his obituary?