Ex-NFL star Vernon Davis says it's still a mystery as to how exactly his brother, Vontae Davis, died earlier this week ... although he said Monday he believes the former Colts cornerback passed away following a session in a sauna.
The ex-San Francisco 49ers tight end broke his silence on his little bro's death during an interview with The Daily Mail on Wednesday ... just two days after Vontae was found deceased inside a gym at his Southwest Ranches, Fla.