In the past few opiate-soaked years, U.S. officials say, nearly all the heroin coursing through American cities has come from one place: Mexico. “There are still a lot of question marks around the figures,” said Martin Jelsma, director of the drug program at the Transnational Institute, a research organization based in Amsterdam, and the co-author of a forthcoming study on Mexican and Colombian poppy production. Equally challenging, Jelsma said, is identifying the source country of a heroin sample. He doubts that the DEA can always tell whether heroin is made from Mexican or Colombian poppy, given that Mexican drug traffickers in some cases have hired Colombians to teach heroin-production techniques, so the product is similar.