New York (CNN) -- Prosecutors said Friday they treating an incident in which a woman allegedly killed herself and her three young children by driving her minivan into the Hudson River as a triple murder and suicide.
"Based on all the information available, there is no one else who can be held criminally liable in this case," said Orange County District Attorney Frank Phillips in a statement.
It may take weeks before the autopsy findings are completed due to the need to receive toxicology results, Phillips added.
The sole survivor in Tuesday's tragic incident was 10-year-old Lashaun Armstrong, who escaped the sinking vehicle where his mother Lashonda Armstrong, 25, as well as his siblings -- an 11-month-old girl, a 2-year-old boy and a 5-year-old boy -- all died.
Police say an investigation into the incident suggests that the mother intentionally drove the vehicle into the Hudson in Newburgh, New York, some 60 miles north of New York City.
The woman who came to the aid of the Lashaun said that the boy was both courageous and terrified.
"He kept saying, 'It's my fault,' " Meave Ryan recalled.
The boy, hoisted himself out of the van's driver-side window Tuesday night, swam to shore and then flagged down Ryan by the side of a road.
Lashaun was waving his arms and calling out "Help me, help me, help me," Ryan said.
"He said, 'Mom just drove the car into the water,' " she added.
Ryan said she and the boy drove to the scene, wading into the water to look for survivors.
Lashaun said his mother "just went crazy," according to Ryan.
"She just speeded up and went into the water," Ryan added, recounting what Lashaun had told her.
The boy eventually recalled to Ryan that, as the car was moving, his mother climbed into the back seat and "had all her children cradled in her arms."
According to Ryan's recollection of her conversation with Lashaun, he quoted his mother as saying, "If I'm going to die... you're all going to die with me."
Lashaun told Ryan that he resisted and broke free, yelling out the window for help.
Ryan said the boy told her that as he was trying to escape, "maybe (his mother) had a break of reality," and she then cried out, "Oh, my God, I made a mistake."
She then climbed back into the front seat, the boy told Ryan.
But it was too late.
It took responders an hour of searching, using dive teams and a circling helicopter, to find the four bodies and the van submerged in eight feet of water, according to Fire Chief Michael Vatter.
Ryan said the boy told her that his mother had been frantic, packing her children into her minivan and racing off, because she thought she was being cheated on.
And before the incident, a relative called police reporting a "domestic disturbance" that police say may have involved the father of Armstrong's children.
That belief is based both on a phone call the relative received in which the relative reported hearing "tussling in the background," and a history of domestic problems in the family, police said in a statement released Wednesday.
Authorities declined to identify the relative.
Police said Thursday that they have ruled out potential criminal charges against the father of the dead children, Jean Pierre.
Police say they had previously arrested Pierre on charges of endangering the welfare of a minor, which stemmed from a February incident in which his 2-year-old son was found wandering the streets shortly after 1 a.m.
The boy was found in cold temperatures, only partially clothed in wet clothing, police said in a statement Friday.
Pierre was arrested three days later on February 10 alongside a woman named Shannel Baez, who police say gave conflicting accounts of being both the boy's babysitter and his mother.
Meanwhile, Newburgh Mayor Nicholas Valentine said Tuesday's incident is certain to have "a lasting effect on this city."
A neighbor, Christine Santos, said she "would never have imagined (Armstrong) to do this to her kids."
"To them little babies. I would have never have imagined. I'm in shock," Santos added.
Ryan said Lashaun -- the lone survivor -- is wracked with guilt that he wasn't able to unbuckle his baby sister or teach his two brothers to swim.
"He blames himself," Ryan said of Lashaun, who told her he only learned to swim last year. "That's the sad part."
CNN's Sheila Steffen and Deb Feyerick contributed to this report.