NEW YORK (Reuters) -UnitedHealth Group was sued on Wednesday for allegedly concealing how backlash from the killing of a top executive was damaging its business, causing its stock to nosedive after the insurer lowered its 2025 outlook.

In a proposed class action filed in Manhattan federal court, shareholders said the insurer defrauded them after the December 4 shooting of UnitedHealthcare Chief Executive Brian Thompson by shifting away from strategies that led to higher-than-average claims denials, without revealing the impact on profitability.

UnitedHealth shares fell 22.4% on April 17, wiping out about $119 billion of market value, after the insurer cut its 2025 forecast for adjusted profit per share to between $26 and $26.50 from between $29.50 and $30.

The insurer cited higher costs in its Medicare business. It had issued the old forecast one day before Thompson's death.

Shareholders said UnitedHealth had previously inflated its stock price by recklessly sticking with its old forecast, even as mounting public anger and an October 17 U.S. Senate report on claims denials caused it to become more patient-friendly.

UnitedHealth had no immediate comment. The insurer has offices in Eden Prairie, Minnesota and Washington, D.C.

Wednesday's lawsuit seeks unspecified damages for UnitedHealth shareholders from between December 3, 2024 and April 16, 2025. Chief Executive Andrew Witty and Chief Financial Officer John Rex are also defendants.

Luigi Mangione has pleaded not guilty to murdering Thompson in midtown Manhattan, and could face the death penalty.

Mangione has become a hero to some Americans who are unhappy with for-profit health insurers that deny coverage for treatments.

The case is Faller v UnitedHealth Group Inc et al, U.S. District Court, Southern District of New York, No. 25-03799.