I don't understand how a suicide can hide their own body. They can only bury themselves partially, there will always be that one arm...
You're kidding, of course! But there are a number of ways a person could commit suicide without leaving a body that would be easily found:
1) A person could climb into a dumpster with a contractor garbage bag, climb into the bag, and then tie the bag shut from the inside. I am certain that this method has been employed often.
2) A person could find an abandoned well or mine shaft, an out-of-the-way manhole, or even a hollow tree and climb into it with a razor or a bottle of sleeping pills. The body might be discovered eventually but perhaps not for decades.
3) A person could find an abandoned house, fill a bathtub in the house with a strong solution of lye, and then climb into the tub. The body would likely dissolve before anyone entered the house.
4) A person could break into a funeral parlor at night, turn on the cremation chamber, and then climb in. If the undertaker discovered any bone fragments in the cremation chamber, he would probably assume that they were from the last corpse that he had cremated.
5) A person could find a mucky area of marshland and burrow into the muck. In a matter of hours the wet muck would ooze back into any holes or depressions created on the surface.
6) Pigs will eat anything. A person could strip naked and climb into a pen filled with large hogs, and he could be fairly assured of being eaten alive fairly quickly. This method would include some risk of not being completely devoured, though. (It doesn't apply in this case, but a person who lived near an alligator swamp could try the same basic approach.)
7) If a person knew that concrete footings for a large building were due to be poured on a particular day, he could climb into one of the holes for the footings, cover himself lightly with dirt in order to avoid being spotted by the workers, and wait for the cement to be poured.
8) A person could break into a steel mill and jump into a vat of molten steel; he would be incinerated almost immediately. It would have to be done when no workers were present. (Someone living in an area with active volcanoes could use a volcano instead of a vat of molten metal.)
9) A person could drown himself in a deep body of water while weighting himself down in such a way that his body wouldn't rise. Care would have to be taken to ensure that no body parts could break free and float to the surface. Climbing into a metal cage with weights might do the trick. The person could position the cage on a paddle board or on the gunwale of a motor boat, lock himself in with the weights, and then shift his own weight in such a way as to make the cage fall into the water.
10) It would be possible to dig a hole and position the soil in such a way that the hole would fill itself back in; the person could position the soil above the hole, perhaps using a board or tarp that could be pulled away from inside the hole. It might even be possible for the person to use explosives to fill in the hole after taking his place at the bottom of it.
These are just a few possible methods that I've thought of; some are more likely than others, of course. I'm sure there are many, many more methods—infinitely more methods—than what I've been able to think of.