Squatting over the corpse, Sherlock gestures imperiously. John, of course, comes running. He drops down next to Sherlock, studying the grisly scene. There's blood splatter all over the floor, and the back of the man's head is smashed in. Sherlock merely nods, waiting for John's input.
He studies the wound for a moment, carefully pulling clotted hair out of the way, before checking the victim's eyes, throat, and hands.
"I'm assuming the fact that his skull is smashed in is the cause of death - I don't see any defensive wounds or signs of obvious trauma on the front, so..." He looks to Sherlock for confirmation, "I would say the perpetrator snuck up on him."
Grinning, Sherlock nods and gestures for John to continue. "That wound was clearly not caused by a bare fist..." he pauses, looking closer. Sherlock hands him the magnifier. "Something very heavy, clearly, but not very precise. The bone is smashed, not cut, but one edge is relatively straight. There's some orange-ish dust in the hair..." John trails off, his face lit up with a sudden epiphany. He darts off to the rubbish pile at the entrance to the crime scene.
Even the look of pride on John's own face can't surpass the one on Sherlock's when John rummages through the pile and unearths a bloody brick.