Inside the Apartment Where 12-Year-Old Garrett Phillips Was Murdered

— -- It was Oct. 24, 2011, when 12-year-old Garrett Phillips was found strangled to death inside his home in Potsdam, New York, a small town near the Canadian border.

Today, Garrett's mother's ex-boyfriend, Nick Hillary, was found not guilty in the boy's murder.

On Tuesday, the eve of the verdict, Interim Potsdam Police Chief Mark Murray took ABC News' Elizabeth Vargas through the crime scene: a 3-bedroom apartment where Garrett lived and where he was found on the floor that fateful October day.

Garrett lived at the apartment at 100 Market St. with his mother, Tandy Cyrus, and younger brother, Aaron. They moved in just months before Garrett died, after Cyrus and Hillary broke up. Tandy and Aaron have since moved out.

The apartment is on the second floor of the roughly 100-year-old building, Murray said. There is only one door to the apartment.

On that rainy afternoon in October 2011, police responded to the scene at just after 5 p.m. after next-door neighbors heard concerning noises from Garrett's apartment and called 911. Police went up the apartment building stairs and into the home, where they found Garrett unconscious and alone inside. Garrett was taken to the local hospital where he was declared dead later that night.

Back at the apartment, the investigation was just beginning. Inside the home that day, "Everything was very clean," Murray said. Garrett and Aaron's school schedules were on the fridge and family portraits were on the wall.

"Nothing in the living room area was out of place," Murray said. "You could see that Garrett had neatly set his sneakers by the closet. His rip stick was neatly propped up against the wall. His backpack was taken off. The only real signs of struggle was his sweatshirt laying in the hallway and his physical body."

In one room, a screen in a window seemed warped, Murray said.

At that point "we weren't sure what we had," Murray told "20/20." "We weren't thinking it was a homicide immediately, but something had happened. You know, outlandish thoughts like, 'Maybe Garrett fell out the window and made his way back up here and died,' ... or an accident happened in the apartment and ... one of the kids didn't wanna get caught or in trouble, so he went out the window. But then when we looked at it closer. That's a remarkable jump from the window."

Murray said the window screen was forced out, with just enough space to fit a body through. All of other window screens in the home were intact, Murray said.

"It became very clear that the only place to get in or out, other than the front door that hadn't been utilized, was this window," he said.

The window is approximately 20 feet above the ground, Murray said. Police suspect the killer jumped out it after strangling Garrett.

But at around 5 p.m., when the murder is estimated to have occurred, no one saw anyone jump or flee from the building. The people who lived downstairs didn't report hearing or seeing anything, Murray said.

"It's very frustrating," he told "20/20." "You would think, like, wouldn't someone hear somebody yelling, or see something or do anything? You've got inclement weather, it's near dusk -- if not dark."

There were people outside changing a tire, but they only reported hearing the window screen being pushed out, Murray said.

"Theoretically, the person making this jump is waiting," he said. "Sees the people down there or hears them changing the tire, and waits until the coast is clear to make the jump."

Police collected fingerprints from the window; they are not Hillary's and have never been identified, Murray said. Police said they tested every person with access to the apartment, including residents and maintenance staff.

No prints or hairs from the scene matched the police's suspect, Hillary. But Murray said, "even if we had collected hairs and fibers [matching Hillary], he had been in the apartment -- he moved [Garrett's mother] Tandy in, he was in the apartment in the middle of the night on a number of occasions. Easily explained." (Hillary has denied visiting the apartment without Cyrus' permission.)

Police canvassed the neighborhood, but no one had witnessed anything, Murray said. "It's a very busy street. But who's looking, you know, 40 yards off, 50 yards off the street on a dark, rainy night for someone jumping out a window?"

He added: "It was definitely frustrating. A roller coaster of emotions. You would send a wave of evidence, you know, expecting a probative piece of DNA, or fingerprint or a hair or fiber ... then just not getting that.

"It was a true tragedy," he said. "It still is."