Jean McPherson’s death by cyanide poisoning is announced in the San Francisco Chronicle on May 30, 1947. (Courtesy photo)

Jean McPherson’s death by cyanide poisoning is announced in the San Francisco Chronicle on May 30, 1947. (Courtesy photo)

The Deadly Gas: A poisonous tale of murder-suicide

It could have been a headline story with casualties in the hundreds. Instead, it was a small item in the back of the paper, a story almost no one knows today …

On the night of May 26, 1947, homicide inspectors Dan Shelley and Al Nelder arrived at 3973 23rd St. to investigate a suspicious death. Inside the apartment, they found the body of Jean McPherson, 27, lying on the floor. A glass smelling of whisky was beside her. A matching smell came from a young man named Al Garson, who was sitting groggily on the sofa.

Garson told police he had come by the apartment around 7 p.m. to pick up McPherson for their date, but no one answered the door. Disappointed, Garson went to a bar and started drinking, coming back twice to check her apartment. At 9 p.m., he entered her apartment through a back window and found her lying on the floor. Attempting to revive her, Garson tried to force a glass of whiskey down her throat. When that failed, he called a hospital. The ambulance drivers then called the police.

But there was another smell, much stronger than alcohol, that permeated the apartment — the smell of cyanide. Detectives found a one-pound container of the highly toxic white powder near the kitchen sink. While searching the living room, they found two glasses, one of which held a milky liquid smelling of cyanide. Detectives sent all of the glasses, bottles and poison container to the lab for fingerprint analysis and reported the case as a “probable suicide.”

The results of the fingerprint analysis the next morning made McPherson’s suicide highly unlikely and eliminated Garson as a suspect. The glass of whisky next to McPherson had only Garson’s fingerprints on it and contained no poison. The glass with the deadly cyanide held McPherson fingerprints and those of an unknown person, most likely the killer.
Garson, once sober, added more detail to his story.

At 5:30 p.m., on his way to confirm his date with McPherson, he had run into her roommate, Theta Dungan, who had served with McPherson in the U.S. Marines during World War II. Dungan told him that McPherson had canceled the date, but Garson decided to check himself and went to the apartment.

Dungan, who had not returned to the apartment, became the main suspect. Fingerprint files from the Marine Corps revealed her fingerprints were on the glass that killed McPherson. A woman who had seen Dungan the previous evening described her as very depressed and suicidal.
“She even suggested that I jump off the Golden Gate Bridge with her,” the woman said.

When detectives learned Dungan worked at the Northwest Exterminating Company, they hurried to the company’s headquarters and talked to her boss, Charles Saul. Saul had no idea where the cyanide powder had come from but said a large can of a much more powerful poison, hydrocyanic acid gas, had been stolen from the company the previous evening. Also missing was the special tool needed to open the can and the canvas carrying bag.

Hydrocyanic acid gas was used in the Nazi extermination camps in Germany during World War II and in San Quentin State Prison’s gas chamber.

“This gas is so lethal that I count the cans every night before I leave work and I count them again as soon as I arrive in the morning,” Saul said. “One can contains enough gas to kill every person in a three-story apartment house.”

It didn’t take much to figure out Dungan had stolen the can of poison gas. She had one of the only two keys that opened the locked area where the cans were kept. Police also discovered Dungan had stolen the gas container after she had poisoned McPherson with cyanide powder. Detectives traced the cyanide powder that killed McPherson to a chemical supply house and learned that Dungan had purchased it under an assumed name.

One mystery had been solved, but a more dangerous question still puzzled police: What was Theta Dungan planning to do with the can of deadly gas?

Dungan was suicidal, but using hydrocyanic acid gas for this purpose would be like using a sledgehammer to kill a fly. Police feared she might open the can of poison gas in an enclosed space, and that the gas would kill many others. Authorities sent descriptions of Dungan to hotels and transportation hubs and notified the newspapers. They also questioned Dungan’s acquaintances to find out her motives for McPherson’s murder and her whereabouts.

After a 10-day search, the only people who hadn’t been contacted were Dungan’s aunt and uncle, who lived in Pepperwood, a town in Humboldt County, 240 miles north of San Francisco. Police phoned the sheriff of Humboldt County and asked him to pay a visit to Dungan’s relatives. The timing of their phone call was uncanny; the sheriff called back an hour later with the news that Dungan’s aunt and uncle had seen her for the first time in four years walking by their house that morning. Dungan, who was carrying a canvas bag, told them she was camping with some friends in the redwoods and immediately walked off.

The sheriff gathered a large search party and headed in the direction she was last seen. Three hours later Theta Dungan’s body was found lying in the hollow of a redwood tree. The open can of hydrocyanic acid was at her feet; the gas had dissipated harmlessly in the open air of the forest.

There is an ironic and historical footnote to this case: In ancient Greece, the word “Theta” was seen as a warning of death and was used to indicate danger, just as the skull and crossbones are used today.

Paul Drexler is a crime historian and director of Crooks Tour of San Francisco. For more information, visit to

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