1)
Why does the Torah insert the (otherwise superfluous) words "Rotze'ach hu, Mos Yumas ha'Rotze'ach"?
1.
Sifri: To teach us that, if the murderer killed the victim by rolling beams or poles on him he is Chayav - even though they are not Keilim.
2)
What is the significance of the fact that the Torah teaches us the Din of someone who kills using metal, a stone or wood?