The dumpster makes sense if Card wanted to leave officials with a DB Cooper mystery. If killing yourself in a dumpster and hoping the contents of the dumpster make their way to the landfill, his body vanishes and officials have a never-ending manhunt.
A other possibility is that either g skitzo, he hid in the dumpster thinking it a good hiding place, but became overwhelmed by what he had done and did himself in. People with mental probl4ms don’t really think very clearly.