The discovery of a dozen plastic milk jugs containing a mysterious yellow-orange liquid in a Brookfield alley on Saturday morning triggered a large-scale hazardous materials response that closed a portion of Ogden Avenue for two hours.

But the liquid, fire officials say, turned out to be a harmless, if obnoxious, cache of urine.

Vehicles from more than half a dozen suburban fire departments and police officers from Brookfield, the FBI and the Illinois State Police converged on the intersection of Ogden and Madison avenues starting at 9 a.m. on May 5 after a resident reported finding the half-gallon plastic jugs placed in various spots in the alley between 4100, 4200 and 4300 blocks of Madison and Arthur avenues.

The bottles appear to have been placed intentionally, said Brookfield Police Lt. Edward Petrak, but so far police don’t have a motive or a suspect for the action.

Fire and public works department personnel collected the jugs and disposed of them, while keeping one jug as evidence.

Eastbound traffic on Ogden Avenue was shut down between 11 a.m. and 1 p.m. said police, as police investigators combed the scene. An Illinois State Police investigator canvassed the surrounding area to try to obtain information about who might have placed the jugs in the alley.

Meanwhile, Brookfield police also directed an FBI agent to the Congress Park train station tunnel to view graffiti possibly related to the upcoming NATO summit in Chicago.