John Errol Ferguson, 65, died at 6:17 p.m., following a lethal injection.
The execution came less than two hours after the U.S. Supreme Court denied a final request for a stay.
Before the execution, Ferguson made a brief but unintelligible statement before 25 witnesses. At about three minutes into the procedure, he moved his head, strained his neck, moved his feet, put his head back down and closed his eyes.
The entire execution took 16 minutes. About three dozen people protested across the street from the prison.
Ferguson and two others were convicted of murdering six people in 1977 during a robbery at in Miami-Dade County house used by marijuana dealers. Ferguson dressed as a utility worker to gain access and let his accomplices inside. Most of the victims were friends who happened to drop by the house while Ferguson and the other men were there. The victims were blindfolded and bound, and the encounter turned violent after a mask fell off one of Ferguson’s gang members and his face was spotted by a victim.
The decision was made to kill all eight people in the house. Two survived. At the time, it was the worst mass slaying ever in Miami-Dade County.