(12-07) 12:46 PST SAN FRANCISCO -- San Francisco police are investigating whether someone poisoned an Inner Sunset family's cat and puppy, one of which was found to have methadone in its system, officials said.

The 1 1/2-year-old cat and 11-month-old puppy died Sunday after falling ill within an hour of each other earlier that day, said their owner, Debi Cournale. Both had been in the family's fenced-in backyard on the 1200 block of 15th Avenue just before they died.

The cat, Cowboy, began "moaning," staggering and vomiting at about 3 p.m., Cournale said. She and her 14-year-old daughter rushed the cat to a veterinarian, then returned about an hour later to find that Dakota, the family's mixed-breed puppy, was also violently ill and frantically running around the home.

They took the dog to the same veterinarian, where he died about 9:30 p.m. The cat was euthanized a short time later.

"It was insane, absolutely insane," Cournale said. "Here's your little puppy, lying on a bed, dead, and on the other side is your cat, lying in an incubator, fighting for his life. It was like a horror movie."

A preliminary in-house urine test found traces of methadone in the puppy's system, said Bonnie Yoffe, an All Animals Emergency Hospital veterinarian who treated the animals.

A necropsy will be performed to determine what killed the animals, but Yoffe said poisoning was likely. Both animals were convulsing when they arrived at the hospital, and Dakota had a high fever.

"They were both presented as if they got into some sort of poison," Yoffe said. "Given that the cat and the dog were both presented so close to each other, it certainly makes toxicity as a cause of death higher on the differential list."

Cournale said there is no way the pets could have ingested something on their own because the family keeps no toxic material.

Police are investigating. Officer Albie Esparza, a department spokesman, warned pet owners in the area to keep a close eye on their pets and report any suspicious activity.

"We're just numb," Cournale said. "I don't know what to say - this happened in our backyard. How safe can you feel when your animals get killed in your own backyard?"