usually it's because they're stupid and blab about it. "returning to the scene of the crime" is such a cliche because they actually do that very often. even smarter ones do, they get paranoid or smug or just want to feel a bit of the thrill again and go back to check out the crime scene while it still has cops standing by watching it. for a while before smart phones were ubiquitous, the trend was for dumb criminals to log into facebook on computers at crime scenes. also leaving assloads of evidence all over the place. take a big old bite of cheese from the fridge when your dental records are known to the government and leave your day job uniform with your name tag still on it on the couch. that level of evidence left behind. someone like this can get away with it as long as he actually leaves and never comes back to the scene.
United States