Michael was driving around flat-broke when he passed his first armored truck, so he shot out the tires and the driver, then jacked the truck and took off with rims ablaze. After a near never-ending two star chase the truck is his, but he only has small arms and can't afford any grenades (stronger munitions are still level-locked).
So how could one break open an armored truck without adequate explosives?
There's the truck. Michael is actually in the driver's seat, the shootout in the back is completely unrelated.
