Police are searching for answers after a teenager allegedly killed five people, including a police officer, and injured two others in a mass shooting along a nature trail in Raleigh, North Carolina.

The suspected shooter, a 15-year-old boy, is a relative of one of the victims killed, according to a law enforcement official briefed on the investigation.

Among the victims was Raleigh police officer Gabriel Torres, 29, who was on his way to work when he was shot and killed, according to Raleigh police chief Estella Patterson.

The four others killed were identified as Nicole Connors, 52 ; Susan Karnatz, 49; Mary Marshall, 34; and James Roger Thompson, 16.

MORE : Raleigh mass shooting: What we know about the victims

The unnamed suspect was taken into custody with life-threatening injuries, according to a memo issued by the Department of Homeland Security and obtained by ABC News. It's not clear if the suspect's injuries were self-inflicted, the memo said.

The suspect was still hospitalized in critical condition as of Friday morning, according to the police chief.

A motive is still unknown, according to Patterson, who told reporters that a five-day report will be released. She would not say what type of firearm was used in the shooting or how the suspect obtained the weapon.

"My heart is heavy because we don't have answers as to why this tragedy occurred," Patterson said during a press conference.