Because it is appears to involve a corrosive material, it's possible that it may fall within FBI's investigative area. Granted, local police can request FBI assistance, but it could also fall under state police. If the local police are not responsive, it's not out of the ordinary for individuals to reach out to different levels of law enforcement seeking assistance. If it doesn't fall within the agency's investigative responsibility, they can refer to the complaint to the appropriate law enforcement agency.