I'm not sure anyone will ever know. I'm not aware of any data on the FDR that will tell.
That should be an easy one, if you have the DFDR data (and the coordinates of the runway). LON / LAT is recorded, the air / ground state as well as radio alt, so that you can determine the position where the aircraft settled within GPS precision (limited by the time step interval of the recording and the precision of the aircraft's transducers).
See
http://www.risingup.com/fars/info/part121-344-FAR.shtml for required parameters, LAT / LON is #39.