Investigators spent the weekend looking into how a four-year-old boy fell to his death from an apartment window in the Concourse Village section of the Bronx on Saturday afternoon.

Neighbors say Gabriel Estevez, seen above, was in the superintendent's apartment at the Morrisania II Apartments on East 161st Street while his mother was at the laundromat.

The fourth-floor apartment did not have window guards.

Witnesses say they heard the boy's screams but could not get to him in time.

"I mean I seen a little kid screaming from the fourth floor, he was screaming out the window. So me and two of my friends ran across the street to try and catch him before he fell. But by the time we got across the street, because of traffic, he already fell on the floor," an eyewitness said. "So we jumped over the gate, he had a lot of grass in his mouth. So we took the grass out his mouth and we gave him mouth-to-mouth and pumped on his chest."

Neighbors say Gabriel had spent his last day alive biking and playing.

"Heartbreaking, because I was there when he was born, I saw him walk. Just to know he's not here in this moment is heartbreaking," said Christian Paulino, the boy's cousin. "He used to go to people and offer them food and candy. He was a generous boy at that age. The family is broken into pieces."

They also tell NY1 there are radiators right below the windows in the apartments, which they say makes it easier for an unsupervised child to step up to the window.