Daniel Penny, 24, will be arrested Friday for killing 30-year-old Jordan Neely in a railway compartment on May 1.
Attorneys believe he had no idea that subduing Mr. Neely would kill him. Neely was held down and choked for many minutes.
Witnesses claimed he shouted at metro riders and asked for money, but he did not strike anybody.
New Yorkers protested when onlookers videotaped the event. A freelance journalist on the train recorded the former Marine grabbing Mr. Neely around the neck for 2:55.
He died in hospital after being discovered unresponsive in the train. The city's medical examiner said neck compression killed him.
According to CBS News, the BBC's US partner, Mr. Penny advised passengers to phone the police during the battle.
New York police questioned and released him on the incident day. However, prosecutors charged him on Thursday.
"We can confirm that Daniel Penny will be arrested on a charge of manslaughter in the second degree," a Manhattan District Attorney's Office official stated.
"We cannot provide any additional information until he has been arraigned in Manhattan criminal court."
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