OP, what do you mean by "if?"
I would take a random business card out of the fishbowl at a restaurant and leave it on a bodies. That would leave them scratching their head.
They'd find you within a week. You're not smart enough to be a successful serial killer. "Well, if it wasn't you, then who left your business card?" A little thought and they'd ask for places the business card was left. A few hours of legwork & they'd be looking at a video of the cash register which just so happened to have footage of the fish bowl near the register.