Why did Belarusian shot putter test positive for steroid?

Nadezya Ostapchuk, a Belarusian shot putter, won the gold medal at the 2012 London Olympics. But she failed a drug test. As a result, she forfeited the medal which was given to Valeria Adams of New Zealand.
Two tests displayed that a steroid’s metabolites presented in her urine samples.
When an athlete is caught taking any prohibited drugs, he/she is commonly sentenced to a suspension of two years. As for this Belarusian shot putter, she received one-year suspension. Why was the sentence lighter? There were certain circumstances that proved the following condition: the Belarusian shot putter didn’t apply any forbidden medicine knowingly.
At the beginning the shot putter blamed his former coach. She confirmed that he had sabotaged her sample.
The Belarusian National Anti-Doping Agency investigated this case. The International Association of Athletic Federation also took part in the investigation. It was defined that Yefimov was guilty. This person added powder of methenolone into food of the shot putter during the last week before the 2012 Olympics. The coach affirmed that he had worried about the shot putter. He thought that this steroid would help to win.
In fact, it is difficult to define why Yefimov has done it. He only made the things worse.
Anti-doping agencies accepted these affirmations. That’s why Nadezya Ostapchuk received only one-year ban.
As for supporters of Valeria Adams, they didn’t believe that the Belarusian shot putter had not applied the steroid intentionally. They confirmed that Yefimov just put efforts to protect the shot putter. They affirmed that Nadezya Ostapchuk had taken steroids under recommendations of her coach.
If the Belarusian shot putter’s performance was amazing several months before the 2012 London Olympics, her coach had to be sure that she would win. Why did he trouble about?