Under a plea agreement the prosecution filed at the hearing, the prosecution and the defense agreed to recommend a prison sentence of 8-14 months and a fine between $4,000 and $40,000.
"If you can kill their children we can kill yours,” Reardon, of Millis, Massachusetts, allegedly said.
The bureau cited spikes in both "reporting on potential hate crimes or other criminal violations" and "hoax bomb and active shooter threats," the latter targeting synagogues.
Eyewitness video showed heavy smoke rising from the area; Buffalo airport cancels all flights as FBI investigates.
The FBI director stressed that while heightened vigilance is required "it is by no means a time to panic."
If convicted, Abuayyash could face up to 15 years in federal prison and a possible $250,000 maximum fine.
The Fremont County sheriff described the scene at the funeral home as “horrific.”