How Luigi Mangione's notebook helped federal prosecutors build their case and what's next as he faces mounting charges

It was writings laid bare in a notebook found in Luigi Mangione’s possession, authorities say, that would help investigators build the federal case against him – a well-planned homicide that involved stalking the movements of his alleged victim, UnitedHealthcare CEO Brian Thompson.

It was writings laid bare in a notebook found in Luigi Mangione’s possession, authorities say, that would help investigators build the federal case against him – a well-planned homicide that involved stalking the movements of his alleged victim, UnitedHealthcare CEO Brian Thompson.

An entry dated Aug. 15, reads: “the details are finally coming together,” according to a federal complaint unsealed Thursday. “I’m glad — in a way — that I’ve procrastinated,” Mangione allegedly wrote, saying it gave him time to learn more about the company he was targeting, whose name was redacted by prosecutors.

“‘The target is insurance’ because ‘it checks every box,’” the notebook read, according to the complaint.

The federal complaint marked investigators’ first public acknowledgment of the notebook, more than a week after its existence was first reported by CNN.

The high-profile case took an unusual turn when Mangione, 26, was hit with new federal charges Thursday, on top of state charges he’s already facing for the executive’s Dec. 4 killing in Manhattan, including for first-degree murder as an act of terrorism. The move appeared to take his lawyers by surprise.

Now, the state and federal trials will “work in parallel,” according to the Manhattan District Attorney’s Office.

But Mangione’s defense attorney Karen Friedman Agnifilo said the new charges – which include murder through use of a firearm, two stalking charges and a firearms offense – “raise serious constitutional and statutory double jeopardy concerns.”