Officers went to the building on July 30 for reports of a suspicious person and found a backpack in a homeless camp behind the former fast food restaurant, according to a statement from the city of San Marcos.
There were several containers in the bag that held components needed for "a clandestine methamphetamine laboratory," police said.
One officer was burned by an “acidic powder” found in one of the containers. He was treated at the scene.
A third party company had to be called in to destroy the toxic chemicals.