A Serial Killer's Regret

The only time I've ever felt regret was after I strangled the last girl.
She didn't deserve to die, but she was there when I needed a kill.
She struggled, clawing my hands and face; she would've died quickly, but unlike the others, she just had to fight!
Taking my time, I'd choke her to the point of death, stop to let her breathe, then I'd begin again. Eventually, she became still.
Being tired, I decided to dump her in the woods; a police cruiser drove by as I dragged her.
Once they'd caught me, I regretted taking my time.