Police said the boy was forced to sleep in an unheated garage while in the care of his father, Michael Valva, an NYPD officer who has been charged with second-degree murder, along with his fiancee, Angela Pollina.
Suffolk County Executive Steve Bellone vowed to investigate how the county's Department of Social Services handled the family's case.
Thomas' mother, Justyna Zubko-Valva, told CBS2's Jennifer McLogan she filed "numerous, numerous complaints" over a three-year period.
"That death was preventable," she said.
Zubko-Valva documented her case during that time, even posting video and audio recordings on social media.
She represented herself in the custody battle and said Valva and Pollina convinced CPS and judges that she was unstable. They were granted custody of Zubko-Valva's three sons, as well as Pollina's three daughters.
"I think you have somebody in this case who obviously knew how to work the system, how to manipulate, and we have to look at whether there's some implicit bias there when you're dealing with a police officer," Bellone told McLogan.
Thomas' elementary school also filed reports.
"Basically starved to death. They were looking for food on the classroom floor, in the garbage. They were coming to school wearing diapers," Zubko-Valva said.
The message at a rally Wednesday in Mineola near the courthouse was Thomas Valva was in terrible danger -- and plenty of people knew it. A review of the case should be unsparing, supporters said.
"This needs to stop now, and if people don't jump on this movement, something is very wrong. Please, we beg, we plead, protect our children," Bay Shore resident Gayelynn DeFilippis said.
"I am demanding justice. Thomas is just a beacon for all the other kids that have gone unheard," East Patchogue resident Inger Molina said.
"An unnecessary death, really unnecessary," added Maria Campo of North Babylon. "We need to find the money to hire more people to help children in need."
McLogan reached out to the judges named for their responses, but they declined, citing pending litigation.
Many are demanding the Office of Court Administration review the actions of the Family Court, Supreme Court, and others in the judicial process charged with looking out for Thomas.
"I'd like to get the baseline facts certainly no later than next week ... then we can determine how much further we need to go in terms of investigation," Suffolk County Legislator Tom Cilmi said.
Both Thomas and his 10-year-old brother, Anthony, were diagnosed on the autism spectrum. Zubko-Valva now has custody of Anthony and her other son.
"Please continue praying for my family, for Tommy, for everybody who is affected by this whole situation. Thank you for your kindness," Zubko-Valva said.
Meanwhile, Valva and Pollina have maintained their innocence. Valva has been stripped of his gun and shield and suspended without pay as the investigation continues.
Visitation for Thomas continues from 7 p.m to 9:30 p.m. at Mangano Family Funeral Homes in Deer Park. It will be followed by a funeral Thursday morning at St. Elizabeth Chuch in Melville.
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