The body of Audrii Cunningham, an 11-year-old girl who disappeared while on her way to school in Texas, was found Tuesday in the Trinity River, according to Polk County Sheriff Byron Lyons.

“Audrii’s body was located at the Trinity River under US Highway 59,” Lyons told reporters at a Tuesday news conference. He later said her body had been taken to the medical examiner’s office in Harris County and officials were awaiting information on her cause of death.

Polk County District Attorney Shelly Sitton said they are in the process of preparing arrest warrants for Don Steven McDougal, 42, adding they believe a capital murder charge will be appropriate.

“Based on all of the evidence that law enforcement has collected, they are in the process of preparing the appropriate arrest warrants,” Sitton said. “At this time, we believe the appropriate arrest warrant is going to be for capital murder in the death of Audrii Cunningham. He is still in jail under an unrelated felony charge.”

When asked by reporters how Audrii was killed, Sitton said, “I cannot speak to that.”

McDougal, a friend of Audrii’s father, gave investigators a list of places he had been to, but didn’t divulge where her body was, according to the sheriff. Lyons added authorities also used cell phone data and video to help find her remains.

McDougal was already in custody after he was arrested Friday night on unrelated aggravated assault charges, according to the sheriff’s office, but had been identified as the main person of interest in Audrii’s disappearance.

McDougal had joined in the search efforts for the missing girl, the sheriff told CNN earlier Tuesday.

“Some of the witnesses have even said that he was in the community and knocking on doors … asking have they seen her,” the sheriff told CNN.

“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.”

CNN has attempted to find attorney information for McDougal and has also reached out to his family for comment.

McDougal lives in a trailer on the family’s property and sometimes took Audrii to the bus stop, the sheriff said.

The family’s home is near Lake Livingston – “one of the largest reservoirs in the state, with 83,000 surface acres,” according to Texas Parks & Wildlife.

Around 7 a.m. Thursday, McDougal and Audrii left the house for the bus stop, authorities said. That was the last time Audrii’s family saw her. She never made it onto the school bus or to school that day.

McDougal hasn’t told investigators whether he dropped Audrii off at the bus stop Thursday morning, the sheriff said. But “I do believe that he is our number one person of interest,” Lyons told CNN.

One of the few clues that has been made public in Audrii’s disappearance might be a red “Hello Kitty” backpack she was supposed to carry to school with her.

“There was enough in it to lead us to believe strongly that it is Audrii’s backpack,” Lyons told CNN.

A “small backpack that likely belonged to a child was located near the Lake Livingston Dam” on Friday, the sheriff’s office said.