What was supposed to be a response to a call about a trespasser in Pasadena, Calif., took an unusual twist when police found an altar with human bones in a backyard, and now they are investigating how they were sold on eBay.

Pasadena police responded to the 800 block of North Oakland Avenue on Sunday after a woman living in the home reported an individual trespassing on her property.

"The officers went there on a whole different call. When they checked the area there was a makeshift altar that included some bones," Lt. Terysa Rojas with the Pasadena Police Department Crimes Against Person's division told ABC News. "The coroner determined them to be human bones."

According to Rojas, the woman cooperated with police and was interviewed while the bones were turned over to the coroner's office.

Investigators say the altar serves a religious purpose for the woman living in the home, more specifically a West African and Caribbean religion known as Santeria. However, throughout the investigation over the past couple of days police learned the woman ordered the bones on eBay.

"There are some sites where you can order human bones or skulls through eBay," Rojas said. "I don't know where they get them or how they get to put them on eBay. That's part of our investigation."

Police say there were not only human bones, but also those of animal heads along with burned incense and candles. While the investigation is still preliminary, Rojas said there is nothing the woman can be charged with due to the religious purpose.