It is possible to dispute that cannabis was indeed being smoked out of that bong, but analysis by a lab is likely to cost more $$ than it is worth. And then you'd have to think up a way to bribe the technician to falsify the results.
Do your parents have money? Is your mom sexy? Most of these local guys have a price. Some of them are just desperately horny. Otherwise they're gonna have to file a written request, write some letters to the Board of Selectmen, mayor, governor, congress... fill out some forms, go through the proper procedures and what not.
Not after 2 months, though. Chief of police is probably smoking out of that bong now, with his kid.