Bassem Masri, a regular presence at Ferguson protests, died Tuesday morning after being found unresponsive on a bus in Bridgeton, authorities say.
The cause of death is pending autopsy and toxicology reports. There was nothing suspicious and no trauma to Masri, according to the St. Louis County medical examiner's office.
Someone on the bus tried to perform CPR. Masri, 31, was pronounced dead at 11:09 a.m. Tuesday at a hospital.
Authorities gave Masri's address as in the 15000 block of Coventry Farm Drive in Chesterfield.
Masri often livestreamed demonstrations online to a national and international audience of people following the reaction to the police shooting of Michael Brown in Ferguson in August 2014.
In November 2014, Masri was among five people arrested as protesters chanted and at times closed South Florissant Road in front of the Ferguson Police headquarters.
Earlier this year, he had announced his intention to run for state representative.