Writings and social media posts help reveal the secret life and troubles of Luigi Mangione, the man accused of killing United Healthcare CEO Brian Thompson in Midtown Manhattan on Dec. 4, 2024, Investigation Discovery says.

Investigation Discovery will premiere its documentary, "Who Is Luigi Mangione?" on Monday, Feb. 17, 2025. In this file photo, Mangione, charged in the fatal shooting of UnitedHealthcare CEO Brian Thompson, is escorted by police, Thursday, Dec. 19, 2024, in New York. AP

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Investigation Discovery's 'Who is Luigi Mangione' premieres tonight - here's where to stream it online for free