A routine traffic stop in Northwest Washington developed into a large two-year investigation that zigzagged across the United States before leading this week to the arrests of more than 24 suspects and the break up of a major PCP and heroin ring.

In the predawn hours Tuesday, more than 200 police officers and federal agents fanned out in D.C., Maryland, Virginia and New York, arresting 21 people and recovering more than 5 gallons of PCP, half a kilogram of heroin, 17 guns and about $355,000 in cash and seizing $145,000 in bank accounts.