WASHINGTON—The Justice Department (DOJ) is suing Walmart, alleging the company unlawfully dispensed controlled substances through its pharmacies, helping to fuel the opioid crisis in America. The civil complaint being filed Tuesday points to the role Walmart’s pharmacies may have played in the crisis by filling opioid prescriptions and by unlawfully distributing controlled substances to the pharmacies during the height of the opioid crisis. Walmart operates more than 5,000 pharmacies in its stores around the country. The DOJ alleges Walmart violated federal law by selling thousands of prescriptions for controlled substances that its pharmacists “knew were invalid,” said Jeffrey Clark, the acting assistant attorney general in charge of the DOJ’s civil division. Federal law required Walmart to spot suspicious orders for controlled substances and report those to the Drug Enforcement Administration (DEA), but prosecutors charge the company didn’t do that. Walmart couldn’t immediately be reached for comment. “Walmart knew that its distribution …