Police say 16-year-old Shayna Ritthaler can be seen on security footage texting before entering a two-door Jeep Cherokee outside a Moorcroft coffee shop on Thursday, Oct. 3.

It's the last time she was seen alive. Ritthaler's body was found six days later in the basement of a Blucksberg, South Dakota home, and a 17-year-old boy has been charged as an adult in connection to her death.

"If anyone has any information regarding the suspect vehicle, a 1994 grey Jeep bearing South Dakota [registration] 49JB63 and its whereabouts or activities; along with that of Shayna in the South Dakota area on October 3, 2019 or October 4, 2019, please contact the Moorcroft Police Department at 307-756-3301 or the Meade County Sheriff's Office at 605- 347-2681," Moorcroft Police Officer Bill Bryant said on his department's Facebook page early Thursday.

On the day Ritthaler went missing, the police department was contacted by Moorcroft High School after Ritthaler did not return from the open lunch period. Other students had reported to school administrators that Ritthaler was last seen walking toward the Coffee Cup.

Surveillance video shows Ritthaler standing at the crosswalk of Country Lane and East Converse Street, apparently texting, around 12:30 p.m. At 12:36 p.m., a grey two-door Jeep Cherokee entered the southwest portion of the Coffee Cup parking lot from I-90.

Ritthaler walked to the vehicle and entered the passenger side. The Jeep then left the parking lot southbound on Highway 16.

The next day, cell phone data indicated Ritthaler's last location had been in Moorcroft on Oct. 3. Her cell phone was apparently deactivated within roughly one minute of her entering the Jeep; her social media accounts have been inactive since that time, and police say no updates were provided to family or friends.

On Saturday, Oct. 5, Moorcroft police officers learned that an unknown person of interest -- the suspected driver of the Jeep -- was located in the area of Lead and Deadwood, South Dakota. The following day, the Deadwood Police Department reported that the Jeep had been found in the Sturgis area and officers spoke to a male subject in Deadwood, but Ritthaler wasn't there.

On Monday, Ritthaler's body was found when deputies and agents of South Dakota's Division of Criminal Investigation executed a search warrant at the Blucksberg home.

Michael Gavin Campbell, 17, was taken into custody that day and made his initial court appearance Wednesday, where he was charged as an adult with second-degree murder. Circuit Judge Kevin Krull set his bond at $1 million, KOTA-TV reports.

Campbell allegedly told investigators that he and Ritthaler had argued before the disagreement turned violent and he shot her, a prosecutor said Wednesday.

Campbell is set to be arraigned Wednesday.