[Spoilers] episode r2-17. Why did lelouch lie?

Why did lelouch lie to suzaku about euphemias death, saying he ordered her to kill the japanese? (When in truth, his geass went uncontrollable and he was going to let the special administrative zone happen, and v.v was the culprit and it was an accident?) Also why did he lie about Shirley's death, when in truth it was rolo's?

What's the point of the entire argument?