Cigna Corp. officials did everything they could to sabotage a $48.9 billion merger with Anthem Inc., including refusing to consider divestitures that would have helped the deal win regulatory approval, Anthem’s general counsel told a judge.

Cigna refused to turn over data Anthem executives needed to convince U.S. Justice Department attorneys of the merger’s value to customers, Thomas Zielinski, Anthem’s top lawyer, testified Monday in the opening of a damages trial tied to the transaction’s collapse.