The 363 FDNY members murdered that day.
The number is actually much higher, given how many first responders have died and will die from related illnesses. (As of 2019 the number if well over 10,000). One recent study showed that first responders are 15% more likely to get a whole range of cancers and illnesses. Carbon Nanotubes Found in the Lungs of World Trade Center Patients and Dust Samples