This extract is worrying - my highlight:
"According to recorded data, as Flight 51 descended below the published altitude, the aircraft’s trajectory generated minimum safe altitude warnings both visually and aurally on the controller’s radar display. At 8:09:16 a flashing MSAW indicator appeared on the aircraft’s data block on the display that continued until the end of the flight. According to the NTSB, the controller was not aware of such warnings nor did he issue any terrain conflict alerts or climb instructions to the flight crew as the MSAW warning continued to report."