TUCSON, Ariz. (AP) — Aaron Francisco Chavez swallowed at least one of the sky blue pills at a Halloween party before falling asleep forever. He became yet another victim killed by a flood of illicit fentanyl smuggled from Mexico by the Sinaloa cartel into the Southwest — a profitable new business for the drug gang that has made the synthetic opioid responsible for the most fatal overdoses in the U.S.

Three others at the party in Tucson also took the pills nicknamed "Mexican oxy." They were saved after partygoers flagged down police who administered naloxone overdose reversal medication. The tr...