MINNEAPOLIS — Researchers believe they found the grave of a man who could be considered the first black male slave freed by Abraham Lincoln, tracking his final resting place to the cemetery of a former Minnesota psychiatric hospital.William Henry Costley was just 10 months old in 1841 when Lincoln, who was still a young lawyer, won an Illinois Supreme Court case freeing Costley’s mother from indentured servitude — a status that historians say would have been akin to enslavement for the black woman and child at that time …