Certain missions require you to open a safe deposit boxes, which take quite a long time to open with a lock pick. I've noticed that there are icons for using a saw and C4 on them, but I haven't unlocked them yet. Is the slow process of lock picking the only way for me to open safe deposit boxes then, or is there a faster method? Perhaps there's a switch or key I can find to open them?
Additionally, assuming their are multiple safe deposit boxes within close proximity of each other, will C4 open several of them or just one?