A Tucson man was arrested on suspicion of first-degree murder and arson of an occupied structure after he was observed throwing an incendiary device at a home on Tucson’s south side Monday, according to the Pima County Sheriff’s Department.

Sheriff’s deputies responded to reports of a structure fire in the area of 4000 E. Benson Highway at approximately 3:50 a.m. They arrived to find a residential structure engulfed in flames, according to a news release from PCSD.

Rural Metro Fire extinguished the blaze. No other structures were damaged.

Through witness interviews, Pima County detectives determined that 53-year-old Fred Arthur Blasch was observed near the home when the fire began, the news release said.

Blasch was seen throwing an improvised incendiary device at the home while all of the occupants were still inside, according to the news release.

The home, multiple vehicles and two cats were lost in the fire, the news release said.

All other occupants of the home made it out safely.

Blasch was arrested and booked into the Pima County Adult Detention Complex.

The investigation is ongoing.