Both Athena and Pallas were fighting for Zeus but for different reasons.
Zeus wanted Athena his daughter to win so he came up with an idea. Pallas liked Zeus and Zeus knew that and used that to his advantage. He flashed his cape called the Aegis and it worked to well. Pallas lost attention in the fight and looked at Zeus and Athena Killed her friend.
Pallas died in Athens hands and instead of the usual feast there was a funeral for Pallas. Athena was not blamed for anything and I was called an accident.
I am so sorry Pallas...
Was Zeus Impressed....?
Zeus knew his part in Pallas's death.
What do you want?
I am sorry Athena...
Zeus gave her the Aegis
And that is the story on how Athena got the Aegis from Zeus. She added onto the cape with Medusa's head and a Gigantes hide.