kill someone dead

Possibly derived from the phrase shoot someone dead.

kill someone dead (third-person singular simple present kills someone dead, present participle killing someone dead, simple past and past participle killed someone dead)

1. (dialect, US) To murder someone and ensure that they are dead.
   • 2005, George P. Matheos, Mirages of the Rub Al-Khali:

     You don't understand, do you Hassan? It's not the Saudis who own all this oil of Ghawar. It's the Americans who own it. And if you try to take it away from them, they will kill you dead like they killed Saddam Hussein dead.

• Often used to sound threatening.