Guillermo Galdos challenges a Puerto Rico dealer who sells fentanyl on the streets. Fentanyl is often found laced in other drugs, so Galdos uses a testing kit to see if other drugs offered by the dealer are also contaminated. WATCH: ‘America’s drug war: Puerto Rico’ on Channel 4 and YouTube now. #PuertoRico #USA #SanJuan #UnreportedWorld