Can a person be impeached after leaving office?

It's a sticky point I know, but here's some of my reasoning.

These guys have committed crimes. Yet, we are obligated as taxpayers to not only pay them for the rest of their lives, but to pay for bodyguards, offices, secretaries, libraries, etc. An impeachment and conviction could relieve the taxpayer of this burden.

Also, and this is even more important, we could be sure that all those that profited from the illegalities are forced to pay for the damage they created, and, imho, forced to pay the families of all the dead soldiers that were needlessly killed. The American corporations that profited in the billions and billions of taxpayer monies should be forced to pay for the damages in Iraq, not our grandchildren.

The only thing I see for sure in the constitution is that an impeached person cannot be pardoned. We are way too close to the end of this administration to expect they'll be impeached before leaving office, so the big legal question I have is can we still have them impeached after leaving office?

The reason for impeachment is to remove a criminal from power. Well, isn't it still power over people when they receive funds for themselves and their staffs and offices after leaving office? And isn't it still power over people when the few corporations that profited mightily from the war siply smile in the sunshine with their non-taxable dollars?

Questions someone must know answers to.