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. 

 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 Conners, 52; Susan Karnatz, 49; Mary Marshall, 35; and James Roger Thompson, 16. 

 Thompson was a junior at Knightdale High School, according to a statement from the principal.

 Police did not say what -- if any -- connection the victims had to the suspect. 

 The unnamed suspect, who local police described as a 15-year-old boy, 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. 

 The shooting remains under investigation and a motive is still unknown, according to Patterson, who told reporters that a five-day report will be released.

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 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. "But what I can tell you is that the Raleigh Police Department and the Raleigh community is resilient and we stand strong and we will heal." 

 The shooting took place in the vicinity of the Neuse River Greenway Trail, near Osprey Cove and Bay Harbor drives in Raleigh. The crime scene spans over 2 miles. The suspect first shot two people in the streets of the neighborhood before fleeing toward the nature trail, where he opened fire, killing three more people and wounding two others, according to Patterson. 

 The police chief told reporters that the arrest of the suspect came after a "long standoff" and was a "team effort" by multiple agencies.

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 A 59-year-old was among the two shot and injured and remains hospitalized in critical condition, according to Patterson. 

 Raleigh police officer Casey Joseph Clark, 33, was also injured; he has been treated and released from the hospital.