The body of a Penn State professor who's been missing for a week has been found in a quarry, and police said Friday they've charged a man with luring him there under the ruse they'd harvest marijuana plants but instead pushed him off an 80-foot cliff.

The remains of Ronald Bettig, a 56-year-old associate professor of media studies, were found Thursday, a week after he was reported missing. Penn State police launched an investigation and transferred the case to Pennsylvania State Police this week.

On Friday, police charged George Ishler Jr., 39, of Pennsylvania Furnace, with first- and third-degree murder and other charges in Bettig's death, according to online court documents.

According to a criminal complaint, Ishler told police during an interview Friday that Bettig recently signed a will, and he believed there was "a possibility of financial gain" for him and a woman who'd been living with Bettig. Police claim he eventually admitted to pushing Bettig.

No attorney information was available for Ishler in online court documents.

Bettig, of Lemont, had recently befriended Ishler and a woman, who police say in the complaint were "known drug users."

According to the criminal complaint, Ishler drove Bettig to the quarry "under a ruse" that he grew marijuana plants nearby and told Bettig they could harvest them. Instead, Ishler pushed Bettig, who fell 80 feet to his death, police said.

Ishler and the woman first told police they had last seen Bettig after they returned home from a trip to Rehoboth Beach, Delaware, on August 12.

Detectives interviewed Ishler and the woman multiple times and heard conflicting statements, police said.

Police found Bettig's vehicle Thursday near the quarry and discovered his body at the bottom of the ravine.

According to Penn State's website, Bettig joined the College of Communications in 1988 and was an associate professor of media studies. He taught courses on the political economy of communications and wrote at least two books on the subject.