What's done in the dark comes to light. (lightswitch)

The lightswitch flipped on, causing light to flood the room, exposing a bloody carpet and walls streaked with blood. Blood dripped out of the closet, covered the bed, and splattered the dresser. Though the detective was used to scenes like this, he'd never seen something this extreme, especially in the quiet neighborhood on 56th street. "My God, what happened in here?"
"Neighbors say they heard screamin' and then soon after they called the us, a car sped outta here like a bat outta hell," the short cop answered.
"License plate number?"
"Nah, apparently the screamin' was so terrifying that they all hid after they called us"
"Anything about the family who lived here?"
"Uh, just two adults. They kept to themselves a lot, not a lot of people knew too much about 'em."
"I'll come back with my crew," the detective said, flipping off the lights and closing the door to the small bedroom. As the detective turned away from the door he glanced at the red stain on the officer's hand. Was he imagining it? He cleared his throat to say something when the officer's walky talky interupted; "Hey, Bill there was a murder on 56th street, neighbors just called it in. Are you done with your break? We can go check it out."
The officer glanced at the detective and responded, "Uh, yeah. Actually, I'm just done the street, meet you there in 15 minutes?"
"Yeah, roger that." the staticky backround went silent. All at once everything started to make sense to the detective, everything was exposed, like a lightswitch flipped on in a room.
"How did you know about the murder before anyone reported it?" the detective asked, though he knew the answer.
"Those people were stirrin' up trouble in this town, no one would suspect a cop would try to get rid of him," Bill answered, slowly creeping toward the detective.
"Why did you bring me here?"
"I knew that if you searched the scene well enough you might be able to trace it back to me." The cop had a gun now and was aiming it at the detective. The detective charged at Bill and they fell to the floor as they fought for a handle on the gun. One gunshot sounded in the air. Bill was gone, he stopped the struggle as he ended up like the family of two had in their own bedroom.
"What's done in the dark comes to light, officer," the detective said, walking down the stairs and out of the door.