Ferguson protest leader Darren Seals, 29, was found shot inside a burning car in the village of Riverview, about five miles east of Ferguson, early on Tuesday.
Police have not determined a motive for the crime or identified any witnesses. It declined to say in which part of Seals' body he was shot.
Seals led protests in the city of Ferguson following the fatal shooting of Michael Brown by a police officer in 2014.
— King D Seals (@KingDSeals) January 8, 2016
Police officers were first called to investigate a burning vehicle in Riverview. "When the fire was extinguished, a deceased male subject was located inside of the vehicle," local police department said in a statement.
Seals, whose last-known address was in St. Louis, was identified as the victim.
Hours before his death, Seals posted on Twitter about Colin Kaepernick, a San Francisco 49ers National Football League quarterback who protested racial injustice and police brutality by declining to stand for the national anthem, and the US presidential election.
In his Twitter profile, Seals described himself as a "businessman, revolutionary, activist, unapologetically BLACK, Afrikan in AmeriKKKa, fighter, leader."
Black rights activists were posting Seals' tweet in which he suggests being threatend by police officers in July.
@LegendaryQueen8 yea 10 detectives pulled me and my 14 year old brother over, pointed guns on us, and told me "choose your enemies wisely"
— King D Seals (@KingDSeals) July 25, 2016
News of his death caused a firestorm on social media with many people linking the incident with history of racial discrimination in the US.
RIP #DarrenSeals. Tragic and sadly not surprising given this country's legacy of Black Carnage.
— PARIS (@paris_gfr) September 7, 2016
Although a prominent Black rights activits, Seals criticised the Black Rights Movement for being "white-owned."
When white elites own and control you're pro-black movement it's not a black movement, it's a white movement in black face #BlackLivesMatter
— King D Seals (@KingDSeals) September 1, 2016
Ferguson, a St. Louis suburb, gained national attention because of rioting after the August 2014 shooting of Brown, an unarmed black 18-year-old, by white police officer Darren Wilson.
Most protests were peaceful, but violence erupted when a grand jury decided not to bring charges against Wilson.
A federal investigation later found patterns of racial discrimination by Ferguson police.