On the video, a teenage boy walking a dog on a leash circles around the Charleston Animal Shelter on Tuesday night, apparently confused about what to do. It is night and the shelter is closed.

After a few minutes, he climbs the shelter's 8-foot-high fence and drops the dog onto the ground on the other side. He then leaves while the abandoned animal looks around, then wanders out of view of the shelter's outdoor camera.

No one found the dog until the next morning, when shelter workers were faced with trying to solve the mystery of who left the dog there, whether its owner was searching for it or if it was a stray.

The 8- to 10-month-old Labrador retriever mix wasn't hurt when she was dropped over the fence. It was one of three recently abandoned at the shelter after hours in the past month. Another dog was left outside Charleston Animal Society locked in a crate in 90-degree weather in the late evening. All are currently healthy and doing well at the shelter.

Leaving animals at closed shelters is illegal in South Carolina, and it keeps staff from knowing potentially useful information that could help animals get adopted or reunited with their owner.

"If an animal is abandoned, we don't know if it's a surrender, if it's a stray or if it's bitten somebody," said Pearl Sutton, Charleston Animal Society's senior director of animal services. "That leaves the animal in limbo. We don't know anything about it and we're forced to treat it as a stray."

A detail as simple as where an animal was found could reunite it with its owner, she said.

In the case of the puppy left overnight Tuesday, shelter officials were able to quickly locate the teen who dropped it over the fence.

The teenager was found by the shelter after surveillance video of the incident was posted on YouTube and someone who knew him contacted the shelter. The teen told shelter officials he thought he was doing the right thing by leaving it at the shelter where he knew it would be cared for. He is now working with the shelter's manager of anti-cruelty and outreach, Aldwin Roman, to learn the proper procedures when dealing with stray or lost animals, Sutton said.

The shelter is still searching for the owner of the dog, which was wearing a red collar with fire hydrants on it.

Reach Amanda Coyne at 937-5592 or on Twitter at @AmandaCCoyne