Think of how many reasons Watzman could be wanted dead for. Whether she was actually blackmailing somebody, or she was just being paid to look the other way, after 11 years maybe she got too big for her britches and started demanding more.
Schiff knew his time is up with the impending memo release. Taking her out of the equation becomes a very high priority. No time was wasted. Maybe he was closing up shop in his district, knowing there would be mucho investigation. (Maybe he's dumb enough to think the white hates didn't have everything on him already.) When Watzman, etc. die, what dies with them? Knowledge and spreading that knowledge. Nothing else.