Two 13-year-old boys in the ski town of Park City, Utah died within 48 hours of each other in September, likely overdosing on a powerful heroin substitute that had been delivered — legally — to their homes by the U.S. mail, and is now turning up in cities across the nation.

Ryan Ainsworth was found dead on his couch two days after his best friend Grant Seaver passed away. “I wish I had been better warned,” sang one of their friends at a massive memorial service. “But now it’s too late.”

The death toll could have been worse, say investigators, since as many as 100 Park City students had apparently been discussing the drug “Pink” on SnapChat and other social media.

“This stuff is so powerful that if you touch it, you could go into cardiac arrest,” Park City Police Chief Wade Carpenter told NBC News. “The problem is if you have a credit card and a cell phone, you have access to it.”

Read the full story on NBC News.