Westchester County District Attorney/AP
06/18/2014 at 12:00 PM EDT
From the age of five days old, Lacey Spears said, her son Garnett often was beset by mystery illnesses for which she sought treatment as she moved across the country, eventually gaining his mother an audience on social media as she wrote about his and her struggles.
It was that growing attention on herself, officials now say, that led Spears, 26, to keep her son sick by feeding him a lethal dose of sodium, causing massive brain swelling that led to the 5-year-old's death last January.
Arrested and charged on Tuesday in Westchester County, N.Y., with one count of "depraved murder" and one count of first-degree manslaughter, Spears pleaded not guilty. The charges carry a maximum sentence of 25 years to life.
"Lacey is completely devastated by the loss of her son and absolutely denies harming her son in any way," her attorney, David Sachs, said in an email to FoxNews.com
But for investigators who reviewed her trail and Garnett's medical treatments through Alabama, Florida, Tennessee and New York, it was a tragic end to the probe of a mother suspected of Munchausen syndrome by proxy, a psychiatric disorder in which a parent causes or fabricates symptoms in a child in order to gain sympathy or the spotlight for themselves.
"This is a very sad day for everyone, but it is a day for justice," Capt. Christopher Calabrese, commander of the Westchester County Police Detective Division, told the media after Spears's arrest. "Justice for the betrayal of the intimate trust between a mother and child; justice for a mother's continual abuse and death of her innocent child for her own selfish psychological needs and financial gain; justice for Garnett."
As far back as 2011, the Florida Department of Children and Families had opened a file on Spears following an anonymous hotline call about her behavior.
Authorities suspect the single mom may have poisoned Garnett on at least two occasions, according to The Journal News
: once before he experienced seizures that sent him to Nyack Hospital on Jan. 17, and again two days later when he had to be transferred to another hospital after his sodium levels spiked.
During the second hospital stay, "The defendant provided the medical staff with a medical history for her son, including extensive medical visits, hospitalizations and invasive surgical procedures," according to a statement from the Westchester County District Attorney's Office obtained by PEOPLE. That history, "coupled with [the] unexplained rise in his sodium levels at Nyack Hospital," launched the investigation.
"During the victim's stay in both hospitals, the defendant shared the room with him," the District Attorney's Office statement said.
Accompanying her son into a private bathroom and using a G.I. tube that had been inserted into her son's stomach, "This mother was intentionally feeding her son salt in toxic levels," Assistant District Attorney Doreen Lloyd said in court.
While the indictment obtained by PEOPLE does not accuse Spears of intentionally killing her child, it states that by showing "a depraved indifference to human life," she "did recklessly engage in conduct which created a grave risk of serious physical injury or death to another person ... and thereby caused the death of such person."
Spears, who is being held without bond, is due back in court July 2.