The body of David Buckel was found in Brooklyn's Prospect Park early Saturday. He left a note in a nearby shopping cart which he also emailed to several news outlets including the New York Times, the paper reported.
"Pollution ravages our planet, oozing inhabitability via air, soil, water and weather," he wrote in the email sent to the Times.
"Most humans on the planet now breathe air made unhealthy by fossil fuels, and many die early deaths as a result - my early death by fossil fuel reflects what we are doing to ourselves," the email continued.
Buckel said he wanted his death to lead to increased action, writing: "Honorable purpose in life invites honorable purpose in death."
Police confirmed to dpa that the body of a 60-year-old man had been found in the park after he set himself on fire but could not confirm the contents of the note.
Buckel was the lead attorney in a lawsuit involving Brandon Teena, a transgender man who was murdered in Nebraska. Hilary Swank won an Academy Award for her portrayal of Teena in the 1999 movie "Boys Don't Cry."
Buckel also served as marriage project director at Lambda Legal, a national organization that fights for LGBT rights, where he was the strategist behind same-sex marriage cases in New Jersey and Iowa.
Susan Sommer, a former Lambda Legal attorney who is now the general counsel for the Mayor's Office of Criminal Justice in New York City, told the Times that Buckel "was all about justice, but he was also all about what it means to be human."
Sommer added, "He was a very smart and methodical lawyer. He knew his craft and his trade and was strategic in how to build the blocks toward a sweeping victory."