They hadn't killed him yet at his first coming. It's at the resurrection they will look on him after killing him.
“And I will pour upon the house of David, and upon the inhabitants of Jerusalem, The spirit of grace and of supplications: And they shall look upon me whom they have pierced, And they shall mourn for him, as one mourneth for his only son, And shall be in bitterness for him, as one that is in bitterness for his firstborn.” Zechariah 12:10 (KJV 1900)