Tobbasco is more my taste
My problem with the "BB theory" (as a cetain director will call it in his soon to be shooting film that Swabby has commisioned) is that most of the smaller BB guns (thus easy to hide and sneak into the park) normally wouldn't fire a type of BB nor at the kind of velocity to get full penetration on that glass. The glass isn't super thick but thick enough that standard "soft air" or CO2 BB guns might chip it but would UNLIKELY not go all the way through it. A pump BB gun that it pumped up enough might fire at the right velocity but would have to fire a steele BB to get all the way through. Those pump BB guns however are large and much harder to sneak in.
My money is on a wrist rocket. Using steele ball bearings and with a W/R of suitible "tension" it could put the ball all the way through glass like that found at the GC Panorama and would be "silent" and easy to conceal.