Could they have been using a dog silencer?

About an hour ago my boyfriend and I were laying in bed with the lights off just quietly talking when his curr dog started whimpering, I mean whimpering like I have never heard. It was unnerving. So we kept the lights off and grabbed the gun and flashlight and ran out the door. (we live in the country, if that sounds odd to you lol) And let me just say that i have known this dog for over three years and I know her temperament and character. She barks at things not excessively but she has been worked with to make us aware of intruders and tree squirrels etc. So, as we shine the light in her fenced in area we see there is nothing in the pen, so nothing harming her directly. but we do hear foot steps in two directions and the dog is staring off in one of them, not whimpering anymore. He fired off two shots and the walking stopped for a a few seconds and eventually was gone. After this fact my boyfriend informed me the previous owner had a serious problem with about three guys stealing from his numerous sheds out back which he still keeps his stuff in and we don't rent. While that scares the crap out of me, I know how to use a gun and I will. However our dog doesn't and I want to know how they kept her from barking? Is it possible they used like a audio frequency dog silencer? Would that be something upon her first hearing it, or it getting close to her would make her whimper like that? Please if you can inform me of any known methods or devices they could have used.... It sickens me they messed with our dog.