A man stalked his victim’s apartment for more than an hour before shooting him dead in the head, authorities in Georgia say.

Nigel Belser, 21, stands accused of murder, aggravated assault and possession of a firearm during the commission of a felony. Atlanta cops say he killed 22-year-old Akash Banerjee, a student at Georgia Tech, at an apartment complex on May 18. But what officials have not said is why or how the pair knew each other, if at all.

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An arrest affidavit obtained by local media outlets says video shows Belser, a student at Morehouse College, sneaked into Banerjee’s building around 4 p.m. on the day in question, walked up to the ninth floor via stairs and turned the door knob on the victim’s apartment. Belser reportedly then stayed inside the building for over an hour.

Banerjee left his apartment for a quick run to a nearby gas station and returned about 10 minutes later. Belser was reportedly hiding in the stairwell as Banerjee came back.

“It appears that something caught [the victim’s] attention, which prompted him to reach out to the door of the stairwell, where the suspect was still hiding,” the affidavit reportedly said. “The victim quickly backs up, as he seems to be startled by his discovery.”

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The victim tried to fight back, but Belser allegedly shot him in the head. Banerjee was able to knock on an apartment door before collapsing.

“There is someone in front of my door lying on the floor,” a 911 caller said. “We heard a loud noise … Come quick because he’s apparently been shot in the head.”

Paramedics rushed Banerjee to the hospital but he succumbed to his injuries on May 20. Police released video of a person of interest the next day. Investigators identified Belser as a suspect and he turned himself into the Fulton County Jail on Sunday, officials said.