Charles Anthony Nelson, also known as "Tony," was allegedly persuaded to fire the gun by his friend Brody Blu Kruckenberg, who is Yardley's son, according to information received by the Grand County Sheriff's Office and included in a jail probable cause statement.
Nelson allegedly told a friend he killed someone, and that the victim was "an illegal so no one will miss him," according to the jail document.
Investigators wrote that they later talked to Kruckenberg and Nelson, who supplied details of the shooting and the dumping of Campos' body.
The two teens were charged as adults Monday in 7th District Court with one count each of first-degree felony murder and second-degree felony obstruction of justice. Both are scheduled for initial hearings on April 23 in the Moab court. Each is being held on $100,000 bail.
Under Utah law, 16- and 17-year-olds suspected of murder can be charged as adults without a hearing in juvenile court.
It is not clear from the jail documents if Yardley was present at the time of the shooting. She told police she had last seen Campos in her bed on March 25.
But the documents allege that after Campos was killed, Yardley cleaned blood from the carpet and wall in the room where he died. Tests later performed by police revealed traces of blood on the wall and the carpet where Yardley had allegedly cleaned.
Yardley also removed mattresses and bedding from the scene, and investigators have obtained a receipt showing Yardley bought a new mattress, according to the jail documents.
Yardley, who was being held in jail on $10,000 bond, had not been formally charged.
Campos was reported missing by a relative on March 29.
Police located the body Sunday after getting a tip from the unidentified informant to whom Nelson had allegedly confessed the killing.
The informant said Nelson claimed that on the day of slaying, Kruckenberg had contacted him saying Campos was asleep and asking Nelson to come over, according to jail documents.
Nelson claimed that Kruckenberg said, "Let's kill him," but that Kruckenberg could not do the killing and asked Nelson to do it, according to the jail documents. "[Nelson] said it was not his deal, but was talked into doing it," the jail documents state.
Nelson then told the informant how he pointed the gun through a crack in the doorway of Yardley's bedroom and shot Campos three times, according to jail documents.