They say the two tried to collect a $10,000 reward offered in the case by falsely blaming a juvenile.
The Columbian reports that police say 19-year-old Ryan Ruge and 18-year-old Chasen Sincavage were arrested Thursday for investigation of second-degree arson and making false statements to police.
Sgt. Scot Boyles says police are looking for a third suspect.
Officials say the string of torched porta-potties began on March 5. In some cases, melted plastic was all that was left.