Without going into all the reasons attorneys act, through their trust accounts, as escrow agents, it needs to be remembered that the money held in escrow in them is never the attorney's.  It is the client's.  That, FWIW, was the gist of the Republican-pushed cases a few years back assaulting the use of interest on funds held in lawyers' trust accounts to fund legal services for the poor.  I forget the name of the case that went to the S.Ct. and (IIRC) held that the interest belonged to the clients and the government's appropriation of it for the legal services constituted a "taking", but that made clear that the client owned the money.

I don't know whether, or to what extent non-ownership of the funds is a defense to a money-laundering charge, but I am sure it has some weight.  

More to the point, the required openness of attorney's trust account records militates against any idea there was a concealment - concealment implying criminality - at issue here.  In the state where I practice (and, I'd expect this is the same everywhere), attorneys are required to keep their trust account records open for audit by the ethics police at any time.  While they're only required to maintain records for a period of years (longer than the civil statute of limitations), they also take note of the fact that there is no statute of limitations for ethics offenses.  I still have all of my trust records since day one, and most lawyers I know do the same.

Conclusion - this case is of a piece with Siegelman, Fieger, and the other political retribution cases this Bush DoJ has brought.