So for my first run with Shadowrun 5th edition I want to start with what seems like a simple courier mission to a Yakuza gang. Mr. Johnson has a package to be transported to the rendezvous point with a Yakuza lieutenant. I want the package to look ordinary and almost impossible to identify because it's actually a bomb. I don't want the hacker or mage or anyone in the party to be aware of it because the Johnson plans to make it explode at the rendezvous. A slight malfunction in the device will delay the explosion to when the group is leaving (hurting the unlucky but nothing serious).
So my question is how can I prevent the players to clearly identify the package as a bomb before the delivery? I don't want to simply explain that for some reason the thing is impossible to identify, I want mechanical ways to explain how to hide this from my players.
Is it even possible to hide completely something?
PS: Even though I'm going to play with the 5th edition I don't expect edition-specific answers. An explanation from any Shadowrun official book can work (please identify the book and the page if possible).