Alexander Kueng was let go from jail on Friday night on $750,000 "bond and conditional release," the media said.
Ex-policeman Thomas Lane was the first to be released earlier in June. His bail was set at $1 million.
Kueng, Lane and another former policeman Tou Thao were charged with aiding and abetting second-degree murder.
Floyd's death in police custody in the US state of Minnesota on 25 May sparked mass protests against racism and police brutality across the United States and worldwide. The man died after Derek Chauvin, a Minneapolis white police officer, pinned him to the ground with his knee for over eight minutes. Chauvin has been charged with second-degree murder.
