So, Chateau, I find that your conclusion about SilkAir being the airline Ty/Aja used to fly into Siem Reap to be correct. Since May 4 was a Ssunday(not a Monday as I reported earlier), then MI616 was available to Ty/Aja. Sicne that would have been their best option once in Singapore that morning, it is very likely that they took it.
                                        SILKAIR WEEKLY FLIGHTS SINGAPORE TO SIEM REAP
 Flight                          Depart                     Arrive     Duration  Stops  Mon  Tue  Wed  Thu  Fri  Sat  Sun       
  MI 616  Singapore 10.20 am  Siem Reap 11.35 am  2h 15m  0                                                          x    
  MI 618  Singapore 4.10 pm   Siem Reap    5.20 pm  2h 10m  0                                                  x    
  MI 622  Singapore 8.40 am   Siem Reap    9.50 am  2h 10m  0                     x               x
  MI 630  Singapore 7.55 am   Siem Reap  11.35 am  4h 40m  1                                            x              
  MI 633  Singapore 2.35 pm   Siem Reap    3.50 pm  2h 15m  0             x                                    x                   
  MI 636  Singapore 1.55 pm   Siem Reap    5.35 pm  4h 40m  1                             x
EDITOR's NOTE - the revision above was the result of feedback from Slowhatch and results in totally different conlcusions.