[4][5] Casper started her professional career as a law clerk for Edith W. Fine and J. Harold Flannery of the Massachusetts Appeals Court.

In 1999, Casper became an Assistant United States Attorney in Boston and was the deputy chief of the Organized Crime Drug Enforcement Task Force starting in 2004.

[6] In 2013, Casper presided over the trial, conviction, and sentencing of Boston's infamous organized crime boss, Whitey Bulger.

A lawsuit brought to require the Archivist of the United States to certify the Equal Rights Amendment as part of the U.S.

[8] On August 6, 2020, Casper ruled that the Plaintiffs did not have standing to sue the Archivist to compel him to ratify the ERA and she therefore could not determine the merits of the case.