Our Hands Did Not Spill This Blood
The Torah gives us a hint as to why Yakov ultimately believed that Yosef was still alive. The Pasuk says, וירא את העגלות, that he saw the wagons, and then realized that the good news was true.
Yosef was reminding Yakov of the last subject that they studied together before he was kidnapped and sold by his brothers.
It was all about עגלה ערופה. This was the situation where a murdered corpse was found close to a particular city. The members of that city must break the neck of a calf and declare, ידינו לא שפכו את הדם הזה, “that our hands did not spill this blood.” This declaration served to exempt the inhabitants of that city, of any wrongdoing.
Rav Elie Munk pointed out the irony of this whole affair. Could Yosef’s brothers declare that their hands did not spill their brother’s blood? On one level, they were certainly guilty. But from the aspect of the overall Divine plan, this is the way it was meant to play out.