Unfortunately, they “normally” keep animal torture a secret, and learn from their “mistakes.” When they finally start taking human lives, they keep that hidden as well, and enjoy thinking they are smarter than the authorities who hunt them.
In these days of mega-scientific forensics and DNA, being a serial killer has a relatively short life span.
Unless you’re a smart crim, remembering to wear a pair of latex gloves and dispose of the murder weapon a distant place away and employing assassin-like methods, then science forensics and DNA won’t mean much, will it.
But BTK (Dennis Rader) had a long, 31 year lifespan from the Otero murders to his arrest.