The conservation of energy says that energy cannot be created, nor destroyed. Does this mean that when matter (containing energy due to e=mc^2) enters a black hole it is spurted out again in a completely different form? But if it leaves the black hole in a different form, would it be possible, theoretically, to say, put back together a book that was sent into the black hole? And if this was possible, would we be able to see what happened to the make-up of the object once it had entered the black hole? 

A laser beam carries energy from a source to a destination.

Let's take a nice smooth clean collimated laser beam (i.e., TEM00 mode Gaussian profile).   With a beam splitter, produce two beams.  Delay one beam by an odd-multiple of a half wavelength.  Recombine the two beams in a second beam splitter.  Due to the delayed path of one of the beams, they will destructively interfere, yielding no output beam.

Where did the energy go?  Or, asking another way, what part gets hot?