(CNN) — The suspect in the death and disappearance of 11-year-old Audrii Cunningham is a family friend who was entrusted with dropping her at a school bus stop the day she vanished and aided in the massive dayslong search for the girl before her body was discovered in an east Texas river Tuesday, authorities said.

Audrii’s family believed the suspect, Don Steven McDougal, was just taking the girl down the street when the pair left her home Thursday morning, but she never made it onto the school bus or into her classroom, and a bag resembling her bright red Hello Kitty backpack was later found dropped near a local dam, according to Polk County officials.

Prosecutors are preparing an arrest warrant for McDougal, 42, and believe the evidence supports a capital murder charge, Polk County District Attorney Shelly Sitton said Tuesday.

Audrii’s body was found in the Trinity River, downstream from the reservoir near where the backpack was found and one of several locations McDougal told investigators he had gone around the time of her disappearance, Sheriff Byron Lyons said.

Information about the condition of Audrii’s remains is not being released at this time, the sheriff said, noting the Harris County Medical Examiner’s Office will determine her cause of death.

The suspect is already in custody after being arrested Friday night on unrelated aggravated assault charges, according to the sheriff’s office.

CNN has been unable to determine if McDougal has obtained legal representation and has reached out to his family for comment on the accusations against him.

McDougal, a friend of Audrii’s father, lived in a trailer on the family’s property and sometimes took the girl to catch her school bus in the neighborhood, according to Lyons. He has been the main person of interest in her disappearance as authorities frantically scoured the rural east Texas town of Livingston – about 70 miles northeast of Houston, he said.

As the search was underway, McDougal joined the effort and was seen knocking on neighborhood doors and asking if anyone had seen Audrii, the sheriff told CNN. But Lyons doesn’t believe his efforts were genuine.

“To me, it simply tells me is that he’s trying to give the appearances that he has no play or he’s not at fault in her disappearance and that (he’s) part of the concerned parties who were trying to locate her,” Lyons said Tuesday.

In the days after Audrii vanished, McDougal claimed in several social media comments that he was not guilty in her disappearance and has “done nothing wrong,” according to activity on a Facebook account appearing to belong to the suspect.

“I’m not guilty,” reads a comment from the account under a post made on the Facebook page “True Crime Society” the day after Audrii was reported missing.

“I was there and was questioned. I am not running or hiding,” McDougal wrote before commenting again and saying, “I have done everything I can to help find her. I have done nothing wrong.”

CNN has sought comment from investigators about the Facebook comments.

Investigators located Audrii’s remains using cell phone records, video analysis, and information from McDougal, Lyons said. To help uncover the body, water management authorities slowed the flow of water from the Lake Livingston reservoir, allowing the river level to recede enough to reveal the remains, he said.

“I express my deepest sympathies and condolences to everyone who knew, who cared for and loved Audrii,” the sheriff said. “We will continue to process the evidence that has been gathered to ensure justice for Audrii.”

Suspect has decades-long criminal history

McDougal has a lengthy criminal history dating back to at least 2003 with convictions for violent crimes and another for enticing a child, according to court records in several Texas counties.

In 2007, he was convicted of enticing a child in Brazoria County, Texas. Court records show he pleaded no contest and was sentenced to two years in prison, but given credit for 527 days.

Online records do not provide details on the specific allegations in the child enticement case, but the offense is defined by the state as “the intent to interfere with the lawful custody of a child younger than 18 years” when a person “entices, persuades, or takes the child from the custody of the parent or guardian.”

McDougal was also convicted in 2010 and 2019 for aggravated assault with a deadly weapon.

The victim in the first case, which led to a four-year prison sentence, told CNN on Tuesday that McDougal, his former coworker, attacked him after being thrown out of his house.

“He showed up with some other friends that I had,” Elic Bryan said. “We ended up throwing him out of the house and he came back with a knife.”

McDougal began stabbing the door before coming back inside, Bryan said.

“He came at me with the knife, and I had my shotgun, and I hit him in the face with it,” Bryan said. “I had no idea he was that kind of person.”

Community heartbroken over Audrii’s loss

After pleading for Audrii’s safe return, her loved ones are now left to grapple with the news of her death – and the criminal investigation of a suspect whom some in her family once considered a friend.

The fifth-grader’s classmates and teachers are also grieving the “tragic loss,” the Livingston Independent School District said in a statement on Facebook.

“While the details of this tragedy are still unfolding, our hearts go out to the entire community during this heartbreaking loss,” superintendent Brent Hawkins said.

Amid the anxiety and uncertainty of Audrii’s disappearance, her mother said she now understands the pain of the parents of missing children who she had only ever heard about on the news.

“There’s not words for it. There is not one feeling you feel. It’s a roller coaster. You are broken, you are mad, you are empty. And right now, I am empty,” Matthews told CNN affiliate KPRC on Friday.

She would never be the same if her daughter didn’t return home, Matthews said.

“She has so many opportunities ahead of her, and she deserves every right to be able to reach those opportunities.”

CNN’s Caroll Alvarado, Andy Rose, Jillian Sykes, Rosa Flores, Sara Weisfeldt and Holly Yan contributed to this report.