Police say the man who surrendered to his parole officer Wednesday in connection with the threats made against New York and Philadelphia police officers is not the man they suspect called them in.

Marcus Shelton, 36, remains in custody on separate, outstanding warrants, police say. 

The investigation into who actually placed the calls is ongoing.

The New York Post is reporting that whoever called in the threats told police that Shelton pledged allegiance to the Islamic State group and threatened to shoot police officers.

Police in both cities say they received threatening phone calls that investigators traced to an address in upper Manhattan.

Before Shelton's surrender, the NYPD's Intelligence Bureau Chief Thomas Galati said police had identified him and wished to speak with him regarding the calls. However, they had not confirmed probable cause for an arrest.

Officials say that Shelton has had several addresses and a history of arrests in New York City. 

New York's PBA President Patrick Lynch urged officers to remain alert and take precautions due to the threats.