Jon saw the exact moment, the moment when Adrin's sword and dagger and body moved in response to Jon's attacks before Jon had yet thrown them.
Jon stabbed Adrin in the chest and watched him die. 
mnli hypothesis: Jon stabbed Adrin in the chest and watched him die.  premise: Jon saw the exact moment, the moment when Adrin's sword and dagger and body moved in response to Jon's attacks before Jon had yet thrown them.