In a statement Tuesday, Toronto's Chris Xuereb is quoted as saying he has done nothing wrong since the Jamaicans hired him in May to provide massage therapy and nutritional help.
Powell, the former 100-metre record holder, and Simpson, a three-time Olympic medallist , tested positive for the stimulant oxilofrine at the Jamaican championships last month.
Their agent, Paul Doyle, contends something in the new supplements the sprinters were taking caused it and "Chris is the one that provided those."
The email quotes Xuereb as saying he was disappointed the athletes are blaming him for their violations.
"It is time the athletes took responsibility for their doping instead of looking around for a scapegoat, whether that person is their therapist, bartender or anyone else," says the email, which details Xuereb's relationship with the sprinters. "Athletes keep using the same story, which is to blame the scapegoat for their own wrongdoing."
Earlier Tuesday, Italian police formally placed Powell, Simpson and Xuereb under criminal investigation for violating the country's doping laws. The move came a day after Italian police confiscated unidentified substances in a raid on the hotel where the three were staying in the northeastern town of Lignano Sabbiadoro, following the athletes' positive tests.
Police told the AP the raids were executed after a tip from the World Anti-Doping Agency. Doyle said he and the sprinters worked in conjunction with WADA on the raid after becoming suspicious that Xuereb might have given them supplements laced with a banned substance. Doyle also said Powell and Simpson were aware of the impending raid, but Xuereb was kept out of the loop.
"Asafa and Sherone have been tested more than 100 times each through their career ... and never turned in a positive test," Doyle told the AP in a phone interview. "Now they change their supplements and the first time they get tested, they have a positive test? It has to be something in those new supplements that has caused it. Chris is the one that provided those.
"We're not saying he did anything deliberate, but it's in those supplements."
In the email statement from Xuereb's account, he is quoted as saying he "did not provide any banned or illegal substances to Asafa Powell or Sherone Simpson."
The statement says all the vitamins Xuereb provided to the sprinters were found to be legal by Italian police.
"I do not know what these athletes were taking in addition to what I suggested to them," the statement said. "Although I suggested certain vitamins to these athletes, it is ultimately the athlete's responsibility to accept or reject my suggestion.
"Unfortunately, it appears that these athletes were not solely following my suggestions or WADA's guidelines. These guidelines are in place so all athletes can have a clean sport. Both athletes are clearly looking for a scapegoat. I am confident, and I have also spoken to researchers and the police, that I have done nothing wrong."
Doyle said that while the sprinters had been led to believe everything they were taking was untainted, he and the athletes should have been more responsible about which supplements they used.
"In hindsight, we should've been given a list, made sure we got a list," Doyle said. "The extent of what I did, I said to (Xuereb) in a text message, that all supplements have to be cleared by me first. He never cleared them with me. He did send them in an invoice that had the names of supplements in there that he had purchased. But that was it. I didn't have the ingredient list."
Also on HuffPost