The incident began just after 8 p.m. Wednesday in Farmingville, when authorities say the boys lifted the concrete cover off the cesspool.
Vanegas-Fuentes lost his footing and fell in, and Calderon-Castro followed in a desperate attempt to save his friend.
The cesspool is about 16 feet deep and was half full of waste at the time. Authorities say Venegas-Fuentes soon lost consciousness after the fall.
A third teen, 16-year-old Samuel Suarez, ran into the house and alerted his father, who called 911.
"I was just trying to help him. I wasn't thinking anything, just trying to help them," Suarez said.
But there was nothing Samuel Suarez could do. The 17 year old told police this afternoon, the heart wrenching details of how he helplessly watched his two best friends disappear down into the cesspool last night.
"We were like brothers. We would chill everyday like brothers," Suarez said.
Suarez told me he didn't know what was down the cement block in his backyard. He was trying to move the slab to use it for the base of a campfire.
Edgar was standing to his left. Eduardo watched from the right.
Eduardo lost his footing and slipped, tumbling into the toxic mix of chemicals and feces.
"He grabbed the sides. He was standing, but he passed out," Suarez said.
Edgar then panicked and jumped into the same hole.
"You could see him drowning and Eduardo doesn't know how to swim, I was going to jump first, but Edgar jumped first, I grabbed a hose and tried to give it to him," he said.
Samuel ran and called 911. Within seconds paramedics arrived, but by then both teens were in grave condition.
Authorities used a 12-foot pole to grab the clothing of one victim and pull him out. They used a roof ladder with hooks to rescue the other.
"With the ladder's hooks, we were able to hook him out, get him out," Farmingville assistant fire chief Ralph Gloria said. "We performed CPR on both of them. Both patients were transported to Stony Brook University in cardiac arrest."
Vanegas-Fuentes was pronounced dead at Stony Brook University Medical Center Thursday morning. Calderon-Castro succombed to his injuries shortly thereafter.
Homicide Squad detectives are continuing the investigation.