Two boys who were reported missing last week and found dead in different rivers in Manhattan may have been last seen playing together at the water's edge, according to a law enforcement source.

Alfa Barrie, 11, and Garrett Warren, 13, were seen together in Harlem between May 12 and May 13 before they were reported missing at different times, according to the New York Police Department. The department's harbor unit found the bodies of the boys several days apart, more than two miles away from one another in the Harlem River and the Hudson River.

Garrett died by accidental drowning and the cause and manner of Alfa's death is pending following an examination Sunday, according to the medical examiner's office.

The law enforcement source said authorities have an account from another teenage boy, who was reportedly at the scene, who says Alfa and Garrett were playing by the water's edge, and that one boy shoved the other toward the water and they both ended up going in.

The third boy saw them briefly but did not see them come up again or climb out of the water. A couple of hours later, he approached an adult, who called 911 and described the scene to police, the source said.

The police called in harbor units and divers but were not able to spot either boy in the water. After a search with boats and helicopters, they continued to patrol the area over the next couple of days.

Garrett was found on Thursday in the Harlem River near the Madison Avenue Bridge, which connects Manhattan and the Bronx. Two days later, police found Alfa's body in the Hudson River near the Upper West Side.

Since there were no video cameras in the area, detectives are working to reconstruct the steps of the boys prior to the incident, the source said.

Alfa was reported missing in the early morning of May 14, and Garrett was reported missing in the afternoon of May 15, police say.

The boys attended separate schools but were believed to be friends. Authorities say they connected the two cases after Garrett was reported missing.

CNN affiliate ABC 7 reported family and friends gathered at a mosque in the Bronx after Alfa's body was found.

Family friend Adhmadou Diallo said the boy was close with his mother and helped out at home. "Every time he gives his mommy a goodbye kiss when going to school -- and that's what happened on Friday when he left," Diallo told the outlet.

ABC 7 reported Alfa was a sixth-grade student at Democracy Prep Public School in Harlem, which released a statement mourning the loss of the "funny, bright, witty, inquisitive, and brave child."

"He will be sorely missed by his teachers and fellow students," the school said. "We also stand in solidarity with the family of Alfa's friend, Garrett Warren. While he was not a student, we understand that this is a difficult time for his community as well and share our prayers with them."