Chilling new details in the disappearance of a 5-year-old boy in Texas describe how the woman who has been arrested in the case hid what is believed to be the child’s lifeless body  a storage unit for weeks before it was ultimately discovered at a local motel, according to court papers released Thursday. 

Theresa Balboa, 29, has been charged with tampering with evidence after investigators found reason to believe she had injured the boy and hidden his body "with intent to impair its availability as evidence," according to a criminal complaint obtained by Fox News on Thursday. 

Investigators discovered a child’s body late Tuesday and believe it belongs to Samuel Olson, who family members said would have turned 6 over the weekend, but are awaiting official confirmation from a medical examiner who will also determine how and when the child died, Houston Police Department Assistant Police Chief Heather Morris said Wednesday.

Balboa, who is the girlfriend of Samuel’s father, had been caring for the boy since April 30 and reported him missing to his dad, who notified police, on May 27, the complaint states. The complaint identifies the victim as being 6-year-old Olson. 

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At the time, Balboa claimed Samuel’s biological mother had taken the boy earlier in the day on May 27. She told responding officers that Samuel's mother and someone dressed as a police officer showed up and took the boy from the home, Morris said.

Theresa Balboa, 29, has been charged with tampering with evidence after investigators found reason to believe she had injured Samuel Olson and hidden his body, according to a criminal complaint obtained by Fox News on Thursday. 

Theresa Balboa, 29, has been charged with tampering with evidence after investigators found reason to believe she had injured Samuel Olson and hidden his body, according to a criminal complaint obtained by Fox News on Thursday.  (Houston Police Department)

But evidence gathered and interviews conducted by police point to something much more sinister. 

According to a chilling statement provided by Balboa’s roommate, Benjamin Rivera, Balboa called Rivera around May 10 and told him Samuel had died, the complaint states. 

Rivera went home to find Samuel lying "unresponsive on the bed," he recalled, according to the papers. He told police he and Balboa moved Samuel’s body to "a bathtub, where he remained for two days," court papers state. 

Rivera told investigators that on May 13, "he purchased duct tape and a plastic tote at a local Wal-Mart," the complaint states. He and Balboa then allegedly "wrapped [Samuel’s] corpse in plastic sheet, placed the corpse in a plastic tote, and placed the tote in Rivera’s motor vehicle."

They then drove the body just over five miles away to a storage unit – where they left it for more than two weeks, the complaint alleges.

Despite the May 27 missing persons report, the case didn’t see any real movement until Tuesday evening, when Jasper Police Department received a CrimeStoppers tip. The tip, according to the criminal complaint, stated that Balboa "was in room #106 at the Best Western Motel" and "was possibly in possession of a missing child described as a six-year-old white male who recently went missing from Houston, Texas." 

Police arrived five minutes later and knocked on the door of room 106 multiple times, but received no response. The room was registered to a man named Dylan Walker, the complaint states. 

Officers forced their way in and encountered Balboa in the bathroom and the smell of what the sergeant on the scene recognized as being "possible decomposing human remains," the document states. 

When officers asked Balboa where Samuel was, she allegedly told them he "was inside the box." 

The box – a "black tote with a yellow lid" – was zip-tied shut on the floor in the room. A child’s body was inside, wrapped in black plastic bags and "secured with duct tape," the complaint states.

Police took Balboa into custody at the motel. 

They later interviewed Walker, the man who allegedly booked the motel room where Balboa was found. Walker, 27, told police Balboa called him on Monday and said "she needed help because she was involved in an altercation," the complaint states. 

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The pair met up in a Walmart parking lot in Cleveland, Texas, where Walker drove Balboa to the storage unit where they "picked up a storage container which had a foul odor," he allegedly said.

They then went to the Best Western, where he checked her in, the complaint states. 

Around 6 a.m. Tuesday, Walker "removed the storage container from the bed of his pickup," the complaint states. 

Surveillance footage shows him "drag the tote into room 106," the document further alleges. He then gets in his truck and drives away. 

Walker allegedly told police he was the person who later reported the tip to CrimeStoppers. 

Speaking to local news station KPRC 2 on Wednesday, his father, Dalton Olson, said he could "barely breathe."

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"I don’t know what’s going on," he said at the time. I found out what happened last night."

Morris said Wednesday more charges are possible once the autopsy is complete. In the meantime, Balboa was being held as of Wednesday at the Jasper County jail.  It wasn't clear whether she had an attorney who could speak on her behalf. She is expected to be moved to Houston in the coming days. 

Fox News' Paul Best and The Associated Press contributed to this report.

If you've got a tip, you can reach Stephanie Pagones at Stephanie.Pagones@fox.com.