Commissioner of Safety and Homeland Security Robert Coupe said there are "120 suspects" in Floyd's murder.
The officer has been identified as 44-year-old Eric Mumaw, who is an 18-year veteran of the police department, according to the Metro police department.
At least 82 inmates remained in the building early Thursday. The standoff forced Delaware to lock down all of its state prisons.
Chief Robert White says investigators aren't sure what motivated the shooting but because the officer was wearing a dark blue uniform similar to those worn by police, he warns officers to be careful.
Officer Fahey was putting flares on the road to divert traffic from an accident in Rocky River.