A security camera in the building showed that Tanimoto tossed a bag, probably containing petrol, at the emergency exit. Tape is also believed to have been used to impede the use of the door. It is believed this was done so that clinic occupants would have a hard time evacuating. Investigators also found evidence of additional traps in the building.[21][22] The suspect was found to possess a knife, and blocked a person who tried to run back towards the elevator. The victims, with the path to the exits blocked by fire, went into inner windowless rooms in the back of the clinic where they died.[16]
When you have someone deliberately setting fires and blocking the escape routes with a knife, you have bigger problems than just one stairwell.