The trio probably hopped the fence around the pool late at night, sliding into the water as most of the people at the Chapel Tower apartment complex were sleeping.

Neighbors found their bodies floating in the water around 3:30 a.m., long after CPR could do any good.

But authorities in Durham, N.C., are still trying to find answers to the biggest mystery surrounding their sudden deaths: What would render the three swimmers unable to save themselves or each other?

Police identified the victims as Abril Yuliana Flores-Ojeda, 15; Brian Manuel Benites, 16; and Luis Enrique Delgado-Romero, 21, all of Durham. They did not live at the apartment complex.

They were all pronounced dead shortly after being pulled from the pool Tuesday morning by police and three men who live at the complex.

Durham police spokeswoman Kammie Michael said in a news release that it doesn’t appear that the victims were electrocuted, though the investigation is continuing.

The pool, which remained closed Wednesday, is a summertime focus for the complex. One resident called it the “life of the place.” Now residents are voicing concerns.

“The kids always want to get in the water and have fun,” Sandra Henderson, who lives at Chapel Tower in Durham, told Raleigh, N.C., NBC-affiliate WRAL. “I just hate that this happened. I really do. I hope and pray that living in a community, everybody will be watchful.”

Investigators told the news station that a total of four people slipped into the pool early Tuesday. Police were interviewing the survivor to determine what happened but have not disclosed what the person told them.

Chapel Tower is a short distance from Duke University and markets heavily to people connected to the school — even offering student discounts and furnished apartments. It’s on the Duke transit loop, including a program that gives people safe rides from the university late at night.

But a key amenity is the complex’s pool, which is eight feet at its deepest. The surrounding area also has free WiFi.

The swimming spot, however, is not just popular with the people who live at Chapel Tower. Teenagers routinely climb the fence and go for late-night dips, residents told WRAL.

The pool also has 24-hour security, but no one reported seeing anyone climb the fence or get into the water overnight.

A maintenance worker told the News & Observer that the pool is closed Mondays and the gate had been locked since at least that morning.

Hours later, a resident said, someone was running from apartment to apartment, banging on doors and screaming. The neighbor, who did not disclose his name to the newspaper, said he called 911, then looked outside. There, he said, a man and a police officer were pulling a body from the water.

The neighbor hopped the pool fence, pulled a person who appeared to be a teenager out of the water and attempted CPR, but the teen was not responsive, the News & Observer reported.

Investigators said the cause of death was drowning but were conducting autopsies to determine what may have happened to the victims just before.

Images from local news broadcasts showed police and crime scene investigators scouring the pool area with flashlights and searching behind blue lawn chairs. At one point, an investigator removed what appeared to be clothing and placed it into a brown evidence bag. They also found beer cans.

Less than two weeks ago, John Williams with the Durham County Health Department had inspected the apartment complex’s pool, WRAL said, and found that it was “in very good condition.”

On June 8, he wrote, the water was clear enough that he could see the bottom, and workers at the complex kept a daily record of the water quality. Nothing was floating on the pool’s surface, and the depth was clearly marked.

“When it was inspected 10 days ago, everything was okay,” Khali Gallman, a spokeswoman for the department, told the news station. “We are awaiting an investigation by the police department to be completed. There has been lots of speculation, but no one knows for sure.”

Last summer, 40 children between ages 6 and 12 were sickened at a YMCA in downtown Durham after pool-cleaning chemicals reacted with each other, causing noxious fumes.

The children’s symptoms included vomiting, respiratory illness and skin and eye irritation, according to ABC News. Six of the children were considered to be in serious condition, but they improved quickly after being treated.

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