I think it was manslaughter.
"Penny maintained the hold after the train had reached its next stop,
Broadway–Lafayette Street, while other passengers held the doors open to prevent it from moving.
During the chokehold, some bystanders gave warnings on Neely's health, with one telling Penny, "You're gonna kill him now", while others helped in holding him down until police arrived Vázquez captured the final three minutes of the hold on video, which shows Penny applying it for nearly a minute after Neely had stopped struggling and gone limp."
And here is something from law enforcement.
"Possibly the most important element of training for the use of chokeholds in law enforcement is the understanding that the subject should always be able to breathe freely. The operator uses his right arm to compress both sides of the subject's neck, assisted by the pressure of his left hand, while his elbow, sharply flexed and centered over the midline, places no pressure on the trachea."