"The announcement that Ken Kratz will resign will have no bearing on their investigation," Keith Sellen, director of Wisconsin's Office of Lawyer Regulation, said. "It will continue to its conclusion, as announced last week, and regardless of whether or not he resigns or surrenders his law license."
Van Groll told state investigators that the first text message from Kratz came 10 minutes after she'd left his office in October 2009, following a meeting at which she detailed the abuse that her boyfriend had inflicted.
Over two days, 29 more messages from Kratz followed, increasing in suggestiveness and at times taking a threatening tone.
Investigators reported that Van Groll felt "afraid that if she doesn't do what he wants, Kratz will throw out her whole case."
Before today's announcement, Craanen had said that he would fight attempts by the Wisconsin governor to remove his client from office, arguing that other district attorneys have done worse and kept their jobs.
The Wisconsin District Attorneys Association and several domestic violence advocates have urged Kratz to step down voluntarily.
The Associated Press contributed to this report.