EDITOR’S NOTE: This story includes graphic details of animal cruelty.

Although Miko was just a little over a year old, the shepherd mix had already grown into his adult frame. He was tall enough that his nose could graze a treat bag on someone’s waist; his once oversized paws now fit his large-breed heritage.

In June of last year, Miko’s owner, Alexander Kostyukevich, sought training for the young dog from someone he’d found on Instagram. He decided to use Happy K9 Academy after a successful session with the owner, Kwong Chun Sit, also known as Tony.

But just days after leaving his dog in Sit’s care, Kostyukevich got a text message that would devastate any pet owner: Miko was dead.

The mysterious death of the young, healthy dog in Southern California would eventually lead investigators on a morbid and disturbing journey to crematories, pet disposal services and a cargo van that reeked of bleach and feces as they continued to uncover more deaths.