An intruder in a Fillmore District apartment complex started a fire that set off sprinklers and sparked an investigation, but it's the odd cause of the blaze that seems most notable.

It was 7:42 p.m. Thursday when the sprinkler system in an apartment complex at Laguna and Eddy Streets went off, soaking residents and their possessions.

Investigators with the San Francisco Police Department made an odd discovery when they investigated the cause of the alarm: According to their report, an unknown suspect broke into 1171 Laguna Street through a back window, then "set a fire (shoe in a cooking pot)."

The "shoe caught on fire," police say, "and caused the sprinkler system in the complex to go off."

As of Friday morning, police hasn't made any arrests, nor did they provide any additional details on possible suspects or a motive.