CNN  — 

A person in police custody on unrelated charges is suspected of involvement in the case of an 11-year-old girl who went missing Thursday in Livingston, Texas, according to local authorities.

Audrii Cunningham was last seen near her home, around 7 a.m. on February 15, and was supposed to catch a school bus, according to the Polk County Sheriff’s Office. But she never got on the bus and never made it to school.

An Amber Alert was issued for her on February 15.

Audrii Cunningham.

A sheriff’s news release describes her as “a white female with blonde hair and blue eyes. She weighs 75 pounds and is approximately 4-foot-1-inch tall.”

“Audrii was last seen wearing black pants, a black hoodie with white lettering, and black high-top tennis shoes,” the release says. “She was also carrying a bright red ‘Hello Kitty’ style backpack.”

Investigators say they 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.

He was arrested Friday by the Polk County Sheriff’s Office on an unrelated charge of aggravated assault.

“Also, yesterday a small backpack that likely belonged to a child was located near the Lake Livingston Dam,” the sheriff’s office said. “This investigation remains active and ongoing.”

In an interview with CNN affiliate KPRC-TV, Cunningham’s mother, Cassie Matthews, said “hard is an understatement” for the pain and stress of her daughter’s disappearance.

“She has a lot of loving family, she has so many people that love her and adore her,” Matthews said. “I am not going to be the same unless my baby is returned to me and neither is her family, any of us, any of her friends, any of the people that she has been connected to in the community.”

Livingston is about 70 miles northeast of Houston.

CNN’s Joe Sutton contributed to this report