Answer:
Amphimedon tells him.
Explanation:
Since Amphimedon was one of the suitors that Odysseus has killed, he meets Agamemnom in the underworld and tells him about what happened. About how Penelope did not refuse attention, but also did not marry the suitors. But once Odysseus came home, he became infuriated with the suitors in his house:
"Once lord Odysseus, who had endured so much, picked up the bow, he strung it with ease and shot an arrow through the iron axes."
