A man walked into an Omaha jail and told staffers that he was involved in his mother's death, police said Friday as officers searched a river and its banks for the woman's missing 5-year-old son.

Roberto Martinez-Marinero, 25, was arrested late Thursday after telling the Douglas County Department of Corrections staff that he had a role in the death of his mother, 45-year-old Jesus Ismenia Marinero, the Omaha police department said in a news release. The statement was vague and did not explain Martinez-Marinero's role in the killing, but it said there were no other suspects.

Marinero's body was found Wednesday night hours after her youngest child, an 11-month-old son, was found alive in a dumpster near a suburban Omaha apartment complex. He was wearing only a diaper and had some bruises, but was otherwise fine.

Investigators believe Marinero's 5-year-old son, Josue Ramirez-Merinero, was thrown into the Elkhorn River at a highway bridge just west of Omaha. The boy was last seen on Tuesday and was wearing a gray shirt and gray sweatpants, police said.

Dozens of searchers scoured the riverbanks looking for the boy Friday as a helicopter searched from the air.

Martinez-Marinero was arrested on a charge of suspicion of first-degree murder and a weapons count in his mother's death after Omaha police detectives interviewed him. He could face additional charges, police said.

"At this point in the investigation, there are no other suspects being sought by the Omaha Police Department," the news release said.

An Amber alert was issued Thursday for Josue, but was cancelled later in the day after the vehicle that police were looking for was found. Even though Josue was not found inside the vehicle and the boy was believed to be in danger, police said Amber alert rules require a definitive description of a vehicle involved in missing child cases.

The Omaha home where Jesus Ismenia Marinero and the two younger boys had lived burned down two weeks ago. Omaha news outlets said the family moved in with a relative after the fire.