“Evidence we found on the ground made it even more likely that the flight path was very close to Lion Air’s,”
I suspect they located the stab trim jackscrew and could tell it's position.
Also :“The FAA is ordering the temporary grounding of Boeing 737 MAX aircraft operated by U.S. airlines or in U.S. territory. The agency made this decision as a result of the data gathering process and new evidence collected at the site and analyzed today. This evidence, together with newly refined satellite data available to FAA this morning, led to this decision," the FAA said.