NEW YORK (WPIX) – The NYPD’s civilian watchdog is investigating why officers decided not to immediately arrest Daniel Penny, the 24-year-old Marine veteran who choked Jordan Neely to death aboard the subway.

A spokeswoman for the Civilian Complaint Review Board confirmed on Friday that a complaint had been filed and an investigation into NYPD protocol is now open.

Penny was charged with second-degree manslaughter in the death of Neely, a homeless man and street performer suffering from a mental health crisis, aboard an uptown F train on May 1. Video captured Penny placing Neely in a fatal chokehold. Penny surrendered to the NYPD and will be arraigned Friday.

There has been a public outcry from some, including Rev. Al Sharpton, about why Penny was questioned by the police and then released when there was a death. Protesters have also questioned the length of time – about 10 days – it took the Manhattan district attorney to bring charges.

Attorneys representing Penny have said he was acting to protect himself and other passengers when Neely began acting erratically on the subway.