A family friend is charged with murder in the death of 11-year-old Audrii Cunningham in Texas

A family friend accused of killing 11-year-old Audrii Cunningham was supposed to take the Texas girl to her school bus stop when they left her home in his vehicle nearly a week before authorities found her body in a river, according to court documents released Wednesday.

A large rock was tied to her body when search teams found it Tuesday in the Trinity River in a rural area north of Houston about 10 miles (16 kilometers) from her home, according to the capital murder criminal complaint filed Tuesday against Don Steven McDougal.

Audrii's family reported her missing on Feb. 15 when she failed to return to her Livingston home after school. Investigators discovered that she never got on the bus to go to school that morning.

McDougal, 42, lived in a camper on the family’s property near the shore of Lake Livingston and had previously taken Audrii to the bus stop or to school when she missed the bus, according to Polk County Sheriff Byron Lyons.

McDougal was arrested Friday on an unrelated assault charge and it was not clear if he had an attorney who could comment on the capital murder case. The justice of the peace who released the complaint did not know if McDougal had hired an attorney yet but said he had indicated he did not want a court-appointed lawyer.

A backpack that authorities believe belonged to the child was found Friday near the Lake Livingston dam. That lake is one of the state’s largest reservoirs and was created with a dam on the Trinity River.

Lyons has said there is “substantial evidence” in the case. He said cellphone data was used to help identify places to look and that the local river authority slowed down the outflow of the reservoir to help search teams that were in the water.

"My heart aches with this news,” Lyons said Tuesday.

Polk County District Attorney Shelly Sitton has not said whether her office will seek the death penalty.

Audrii lived with her father, grandparents and other family members, authorities said.

Court records from Brazoria County, south of Houston, show McDougal pleaded no contest in 2008 to two felony counts of enticing a child and was sentenced to two years in prison.

The sheriff said Audrii's body was taken to the Harris County medical examiner’s office in Houston to determine the cause of death.

A candlelight vigil was held for Audrii on Wednesday evening in Livingston on the grounds of an outdoor venue.

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Associated Press writer Sean Murphy contributed to this report from Oklahoma City.