"Yefimov confessed that he added the banned drug metenolone into Ostapchuk's food because he was worried by her unimpressive results ahead of the Olympics," Vankhadlo told the press.
"Yefimov said that he did it at the training base in Belarus just days before the start of the Games without Ostapchuk's knowledge."
Ostapchuk became the first medallist disqualified from the London Games for doping and was stripped of her women's Olympic shot put title.
The International Olympic Committee (IOC) awarded gold to Adams after Ostapchuk provided two urine samples which were both found to contain metenolone.
Russia's Yevgeniya Kolodko was upgraded to silver medal position, with Lijiao Gong of China taking bronze.
Vankhadlo told Belarusian state media belTA that Ostapchuk had already returned the gold medal to the International Olympic Committee.
Adams said on Twitter said she is only just hearing of the news the medal has been returned to the IOC but "it's a great sign, I hope".
Ostapchuk had been competing in her third Olympics in London. She finished fourth in Athens in 2004 and won bronze in Beijing four years ago.
- Newstalk ZB/nzherald.co.nz