Luigi Mangione Poses in New Photo From Inside Brooklyn Jail

Luigi Mangione looks like he's fitting in at the Brooklyn detention center where he's awaiting his murder trial ... because he's posing with some fellow inmates -- and his latest photo goes hard.

Check out this new pic of Luigi mugging for the camera in the yard at MDC Brooklyn ... he's crouching down in front of a brick wall, smiling and throwing up a shaka hand sign.

Luigi's got a watch on his wrist and he's wearing gray and white sweats ... with white socks and what appear to be loafers.

Next to Luigi, another inmate in a gray sweatsuit and black sandals poses too ... and Luigi's buddy is tatted up.

Luigi's been locked up at the notorious federal detention center since December, when he was extradited to New York from Pennsylvania ... and he's facing murder charges for the shooting of UnitedHealthCare CEO Brian Thompson. He's pleaded not guilty.

Diddy's also being held at the same facility while he awaits sentencing for his conviction on prostitution charges in his criminal case ... the two are housed in different cell blocks, and it looks like Luigi's made other friends.

BTW, if you're wondering how Luigi got his swag, the MCC commissary lists items for sale inside, including watches, sweats and loafers. As we know, Luigi's been getting all kinds of monetary donations ... looks like he's been shopping.