Complex sentence: He died in prison on March 28,2016, at the age of 81 and after having served 52 years, making him one of the longest-serving inmates in the New York State prison system.
Split into simpler sentences: He died in prison on March 28,2016, at the age of 81. He had served 52 years, making him one of the longest-serving inmates in the New York State prison system.