Larry Frankel was found by police lying face down in the creek Friday morning. He was dressed in jogging clothes, local blog reported Monday.
Frankel had been missing since at least Wednesday, the DCist blog reported. He is believed to have died of natural causes, The Hill reported.
Relatives and friends confirmed Frankel's death in a Philadelphia Inquirer obituary. He was the executive director of the ACLU of Pennsylvania.
Pennsylvania Gov. Ed Rendell released a statement calling Frankel "one of the most effective advocates for civil liberties and justice in Pennsylvania."
"I could count on Larry for his strategic insight and clever approach to advocacy making him a pleasure to work with and a gentleman that I always wanted on my side," Rendell said.