They prob used a spark plug.... heard those break good, and make almost no sound..... not that i would know personally, but so i've heard..... or didn't hear... lol.
Yea thats what I figured. Thats what I use to use when I stole ****. Theres 2 ways to shatter it silently nearly, flat screwdriver in the seal, or a sparkplug. Must have been a smart thieve, they did it on a night where it thundered and stormed all night so no one heard them..