New York prosecutors are taking a new step to build their case against the man charged in the murder of 50-year-old Brian Thompson, the CEO of Minnesota-based UnitedHealthcare.

Luigi Mangione’s lawyer says he intends to plead not guilty.

Sources tell ABC News that prosecutors are now presenting evidence to a grand jury as they work to secure an indictment against Mangione, as an indictment would strengthen the case for extradition to New York – which Mangione is fighting.

The 26-year-old Ivy League graduate from a prominent real estate family allegedly wrote about his criticism of corporate America and the U.S. healthcare system. A UnitedHealthcare spokesperson confirms that Mangione wasn’t a customer of its insurance system.

Meanwhile, a woman told ABC News she spent time Mangione last year while vacationing in Hawaii, saying they attended a book club and played volleyball, adding Mangione showed no signs of the severe back injury he once described as debilitating.

“I would say he’s a winner and everything, even in volleyball. He wanted to be the best. He always wanted to win. Book club – he wanted to be the one who actually read the book, who had the best answers and questions for everything. He’s a winner all around,” said the woman.

The San Francisco Chronicle is reporting a San Francisco officer recognized Mangione from the images police had released, and that officer alerted the FBI four days before his high-profile arrest.

Mangione’s face was known to police in California because he had been reported as missing by his family just weeks earlier.

His extradition hearing is currently scheduled for Dec. 30th.

CLICK HERE for all of KSTP-TV’s reporting of Thompson’s murder and the case against Mangione.