ST. LOUIS (AP) — The street version of fentanyl blamed in the deaths of thousands of Americans is also threatening police officers, forcing changes in long-standing basics of drug investigations, from confiscations to testing and undercover operations, law enforcement officials say. Overdose deaths have surged as drugs such as heroin, cocaine and counterfeit prescription pills are now commonly laced with fentanyl to increase potency, though drug investigators say it is increasingly sold by itself, too. Fentanyl can be absorbed through the skin or inhaled if it becomes airborne. Because such a small amount can be deadly, police agencies big and small are changing the way they go about keeping officers safe. James Shroba, special agent in charge of the Drug Enforcement Administration's office in St.