Complex sentence: Purdue shows Dana Scully a video of Barnett's capture years earlier, which shows that Mulder didn't fire on Barnett due to him having a hostage, per FBI regulations.
Split into simpler sentences: Purdue shows Dana Scully a video of Barnett's capture years earlier. The video shows that Mulder didn't fire on Barnett due to him having a hostage, per FBI regulations.