(I'm just assuming Bumblebee was the one who killed the others)

"Bumblebee," Optimus said in shock and horror as he looked at his fallen comrades who all lied on the ground- unmoving. "Why...?"

Bumblebee looked up at Optimus- the fire behind him illuminating his ominous figure and the battle mask that hid his expression.

He merely stayed silent as he gently wiped the smeared energon from his battle mask.

"It's not enough," Bumblebee then muttered- before he lunged at Optimus with his energon stained servo reaching out toward him.

:)