A chemical cloud that wafted over the northwest side of Tucson and led to evacuations was the result of a hate crime, the Pima County Sheriff's Department said.

Deputy Dawn Barkman said investigators found several dead animals near the front door of a home, and said the garage and front door had been sealed with a spray foam.

She also said an incendiary device was found at front door garage area, and a "chemical dispersal device" was at the back.

Deputies and a hazardous materials team were on the scene before dawn Sunday and continued collecting evidence throughout the day, Barkman said.

A gas cloud had spread over the area early Sunday, prompting officials to warn people to stay indoors.

A large part of the substance was chlorine mixed with something else that formed the cloud of gas, Barkman said. The gas dissipated by afternoon but Barkman said 13 homes were evacuated as a precaution.

The incident is being jointly investigated by the Pima County Sheriff's Office and the FBI.