What we know about Audrii Cunningham, the missing girl who vanished after she left for school

(CNN) — The only trace in Audrii Cunningham’s disappearance might be a red “Hello Kitty” backpack she was supposed to carry to school with her on Thursday.

The 11-year-old from vanished after she left to catch the school bus Thursday morning in the small, east Texas town of Livingston. She never made it onto the bus, the Polk County Sheriff’s Office said. But “a small backpack that likely belonged to a child was located near the Lake Livingston Dam,” the sheriff’s office said.

Livingston is about 70 miles northeast of Houston.

Now, a man who was arrested for an unrelated aggravated assault case is believed to be “one of the persons of interest involved in the disappearance” of Audrii, the sheriff’s office said. But the girl’s whereabouts remain a mystery.

Here’s what we know about the case:

She never made it to school that day

Audrii was last seen around 7 a.m. Thursday near her home on Lakeside Drive, the Polk County Sheriff’s Office said.

The home is close to Lake Livingston – “one of the largest reservoirs in the state, with 83,000 surface acres,” according to Texas Parks & Wildlife. “The lake is an impoundment of the Trinity River, and provides water for the city of Houston and other East Texas cities.”

“Audrii should have caught the school bus at her neighborhood bus stop; however, school officials reported to the Sheriff’s Office that the school bus did not pick Audrii up, nor did she report to school,” the agency said.

Audrii’s family reported her missing after she didn’t return home from school. A multi-agency search ensued, including the Texas Rangers, the Texas Department of Public Safety, the Livingston Police Department, the Texas State Guard and several local fire departments, the sheriff’s office said.

Her backpack may have been found

On Friday, “a small backpack that likely belonged to a child was located near the Lake Livingston Dam,” the Polk County Sheriff’s Office said.

Previously, authorities said Audrii was carrying a bright red “Hello Kitty” backpack.

But the investigation “remains active and ongoing,” the sheriff’s office said.

‘Foul play may be a factor’

Investigators have identified a 42-year-old man “as one of the persons of interest involved in the disappearance” and believe his dark blue 2003 Chevrolet Suburban was involved, the sheriff’s office said.

The sheriff’s office arrested the man Friday on an unrelated charge of aggravated assault. Authorities have not released details on how the man might be connected to Audrii’s disappearance.

“Our primary focus and hope is that we bring Audrii safely home,” Texas DPS spokesperson Lt. Craig Cummings said. “But we also realize that foul play may be a factor.”

‘This is the stuff you see on TV’

Audrii’s mother, Cassie Matthews, said her heart always broke for the parents of missing children whom she heard about on the news.

“This is the stuff you see on TV, and you can only imagine what the family and the parents are going through,” Matthews told CNN affiliate KPRC.

Now, she’s one of those parents.

“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 said.

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

Audrii is White with blonde hair and blue eyes. She stands about 4 feet, 1 inch tall and weighs about 75 pounds, the sheriff’s office said. The girl was last seen wearing black pants, a black hoodie with white lettering and black high-top tennis shoes.

Anyone with information in this case is asked to immediately contact the Polk County Sheriff’s Office at 936-327-6810 or submit an anonymous tip online.