A Colorado Springs woman has a warning for pet owners to be vigilant if your pets spend time outside. She believes someone threw a poisoned treat into her backyard, killing her dog.

Shannon Collamore is still in shock after losing her eight-month-old Great Dane puppy, Sterling.

"She was always happy and she was always wanting to play," said Collamore. "It's really hard. I'm paranoid to let my two other dogs outside now."

Collamore lives near Constitution and Circle, not far from Wasson High School. She believes a stranger was walking along the alley behind her house, and threw a poisoned treat or piece of meat over the fence into her backyard.

"We think that it was just a random passerby that just wanted to be cruel," said Collamore.

Collamore's mom was watching the dog at the time, and took her to the Cook Veterinary Hospital. Dr. Carin Ramsel tried to save Sterling, but it was too late. She believes the dog ingested rat poison.

"What it does is it prevents them from forming blood clots," said Ramsel.

She has heard of several other cases around town, and says there are key symptoms to watch out for.

"Any change in activity, if they're becoming more lethargic. If they are showing signs of any problems breathing, they're panting and there's no reason for them to be out of breath," said Ramsel. She also suggests checking the animal's gums. If they are not pink, call the vet right away.

As for Collamore, she is devastated by her loss and hopes her message could save someone's pet.

"Walk through your backyard and check to make sure nothing's out of the ordinary back there," said Collamore.

11 News made calls to police and the Pikes Peak Humane Society. Officials say they haven't received any reports of dogs being poisoned in Colorado Springs, but they encourage pet owners to report it.