Mary Ann Plett was a 29-year-old woman, a married mother of two, and a real estate agent with Graham Realty Ltd. in Edmonton, Alberta. On September 15, 1971, she left to meet a prospective buyer who called himself James Cooper and wanted to see an acreage in the Looma area, roughly 30 kilometres southeast of Edmonton. Cooper was described as a large man in his forties with a low, rough voice.
He claimed to work for a pumping company in Winnipeg and said he was interested in purchasing property around Edmonton. Plett left with him for the showing and was never seen alive again. Although September 15 has generally been associated with her homicide, the precise time and cause of her death could not later be established from her remains.
Her disappearance immediately raised concern because the man calling himself Cooper proved impossible to trace. Investigators searched the Looma property extensively, combing the acreage and even draining a large slough in an effort to find evidence. The search was described at the time as one of the largest ever undertaken in Alberta. Police questioned several people whose names were similar to the one Cooper had given, but none could be identified as the mysterious client who had arranged the appointment.
Two days after Plett vanished, her locked automobile was discovered abandoned at a used-car lot in south Edmonton. Investigators found two small human bloodstains inside along with a crumpled wig similar to one she owned. Other accounts of the investigation indicated that blood consistent with her blood type was found in the trunk area and that the vehicle showed indications it may have been driven away from paved roads. The discovery strengthened suspicions that something violent had happened after she left Edmonton with the supposed buyer, but there was still no sign of her.
The investigation shifted dramatically weeks later. On October 30, hunters came across Plett's briefcase along a remote lumber road in the Fort Assiniboine area, about 160 kilometres northwest of Edmonton. Police mounted another extensive search through the heavily wooded countryside. Search dogs located additional property connected to her, including real-estate documents and personal items concealed beneath logs. The papers included material from Graham Realty and information concerning properties she had been handling. Snow eventually forced investigators to suspend the search for the winter.
When the snow disappeared the following spring, the case took its most disturbing turn. On April 14, 1972, workers performing drainage work near Fort Assiniboine discovered pieces of clothing belonging to Plett along Goose Lake Road. Police returned to the area, and on April 19 a search dog located her skull and additional skeletal remains near the general area where her belongings had previously been found. The remains were too decomposed for an autopsy to establish how she had been killed. As a result, investigators were left without a medically determined cause of death and without forensic evidence capable at the time of identifying her killer.
Attention remained focused on the unidentified man calling himself James Cooper. Investigators regarded him as crucial because he had arranged the property showing and was the last known person connected with Plett before she disappeared. Reports indicated that Cooper had been unusually insistent about dealing directly with her and did not provide a reliable telephone number at which he could be reached. Not long after Plett vanished, another Edmonton real-estate agent reportedly received a suspicious call from a man with a similarly deep or gravelly voice who identified himself as “Dave Cooper” and sought a rural property showing, further raising questions about whether the name Cooper had been an alias used to approach agents.
Investigators pursued other possibilities over the years. A man already in custody who had been considered a suspect in the deaths of other Alberta women was reportedly interviewed in connection with Plett's killing. Police and media also examined whether her homicide might have been connected to a suspected serial offender blamed for the deaths of several hitchhikers in Alberta. Those theories produced no charge, and no publicly identified suspect was ultimately tied to her death through evidence sufficient for prosecution.
Despite the enormous search effort, numerous interviews, and decades of attention to the case, the real identity of “James Cooper” has never been established publicly. No one has been arrested, charged, tried, or convicted for Mary Ann Plett's homicide. Her killing remains unsolved, with the mysterious prospective buyer who arranged her final known real-estate appointment still at the center of one of Edmonton's longest-running murder mysteries.
