Italian police confiscated unidentified substances in a raid on Monday at the hotel where both sprinters were staying.
Simpson and Powell’s agent Paul Doyle said over the weekend that both tested positive for the stimulant oxilofrine at the Jamaican championships.
Powell helped the Jamaicans to the 400-meter relay gold medal at the 2008 Olympics and was the last man to hold the individual 100 record before Usain Bolt broke it earlier that year.
Simpson won Olympic gold in the women’s 400 relay in 2004 and silver in 2012, along with an individual silver in the 100 in 2008. Powell released a statement saying that he is cooperating with law enforcement to discover how the oxilofrine got in his system.