Officials say video shows ex-NBA player Elden Campbell went out on the waters in the middle of the night before his tragic drowning ... but he seemingly took some safety precautions, as he was wearing a "partially unzipped" life vest when his body was found on the shore.
TMZ Sports has obtained the investigation report on the NBA champ's death ... which states 57-year-old Campbell left a nearby boat ramp alone around 12:37 AM on Dec. 1.
The docs say Campbell's body was found in the sand along the water's edge in Pompano Beach, Florida .