WARM SPRINGS, Ore. -- Police Chief Carmen Smith says he knows three things about suspected drug trafficker Artemio Corona: He's from Mexico, prefers a Glock .40-caliber handgun, and is quite possibly growing marijuana on the Indian reservation that Mr. Smith patrols.

Last year, Mr. Smith's detectives identified Mr. Corona as the alleged mastermind behind several large marijuana plantations on the Warm Springs Indian Reservation in central Oregon. These "grows," as police call them, had a harvest of 12,000 adult plants, with...