Daniel Vance Walls, 45, of Bainbridge and Mark L. May, 51, of Peebles, have pleaded guilty to charges of conspiracy to distribute and possess with intent to distribute more than 100 kilograms of marijuana from late 1997 through March 2008; and attempted possession with intent to distribute more than 100 kilograms of marijuana on Oct. 17, 2004. They are the last of 38 defendants apprehended due to charges filed in a series of indictments beginning in Oct. 2004 through Feb. 2009, as part of a large-scale drug trafficking investigation in south central Ohio. All others apprehended as part of the investigation have pleaded guilty.