. . .

So by all means, follow your conscience.  If you care enough to do the work required to determine whether or not 1L2JsXHPMYuAa9ugvHGLwkdstCPUDemNCf actually does contain stolen coins, and you have the opportunity to include or exclude a transaction from that address (or one of the addresses to which its coins have been distributed) in a block you're solving, think about how the respect for property rights has helped humanity in the past and consider keeping that tradition alive.

On the possibility that Bitstamp secretly cooperated with the thief in order to embezzle $5M, consider waiting for them to publish something like what I suggested above.

In a world where the things we need and use go bad, sharing comes naturally. The hoarder ends up sitting alone atop a pile of stale bread, rusty tools, and spoiled fruit, and no one wants to help him, for he has helped no one. Money today, however, is not like bread, fruit, or indeed any natural object. It is the lone exception to nature’s law of return, the law of life, death, and rebirth, which says that all things ultimately return to their source. Money does not decay over time, but in its abstraction from physicality, it remains changeless or even grows with time, exponentially, thanks to the power of interest.

The United States of America has a standing military for that same reason it is no longer a confederation.