Investigators are trying to determine what caused a New York Police Department van to crash early Sunday morning in the Bronx.

Police Officer Michael Williams was killed when he was ejected from the right rear passenger seat window after the van struck a jersey barrier on the Bruckner Expressway at about 5 am. Eight other officers were hospitalized but their injuries were not considered to be life threatening.

Mayor Bill de Blasio offered support when he visited the 47th precinct in the North Bronx, where the officers are stationed. De Blasio said that Officer Williams had just graduated from the Police Academy.

"We lost one of our finest, and we lost one of our newest members of the finest, and that hurts even more," de Blasio said.

Police Commissioner Bill Bratton said the 25-year-old officer is the son of a veteran police officer in the Putnam County town of Carmel.

"Michael's father, as a cop for 32 years, has probably seen it all, but never expected to see something like this involving his own son," Bratton said.

The officers were headed into Manhattan for a United Nations security detail when the crash occurred.

With reporting from the Associated Press