Following the angle of the trajectory of the bullet, it must have been shot from the top floor of a building on Rama 4 which is under construction and within the army held area. See <a href="//commons.wikimedia.org/wiki/File:2010_0517_Soi_Ngam_Duphli_04.JPG" title="File:2010 0517 Soi Ngam Duphli 04.JPG">File:2010 0517 Soi Ngam Duphli 04.JPG</a> for a photo of two holes making it clear what the trajectory of the bullet must have been.
<a href="//commons.wikimedia.org/wiki/User:Takeaway" title="User:Takeaway">Takeaway</a>
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<span class="int-own-work" lang="en">Own work</span>