I have reasons to believe that my relative, a deceased US citizen who had Alzheimer's was subject to elder abuse. I don’t live in the States nor have the means for a lawyer. I look forward making a formal complaint, and would appreciate any suggestions.
You could also contact the local police department in the area where your relative lived.
If the alleged abuse was financial, make sure that you have records and data to provide to an investigator. This could be much more difficult in that your relative is no longer here to be examined.
I am sorry for your loss; it must be so much harder to deal with when you're in a different country.