From the November 8, 1935 edition of the Florida Lake County Citizen, a story about a mysterious man who apparently sprays some weird gas into people's homes that puts them to sleep - after which he robs them. The article notes the police had been vexed by such incidents for the previous five months, with it all starting in May.
That is, unless, you want to go back to December 22, 1933, when the first of a series of bizarre incidents involving "The Phantom Anesthetist of Botetourt County, Virginia" began. Here, an unknown man - some say a man and a woman together - went on a similar spree of gassing people within their homes. This gas, however, had varying effects - some it subdued, some it merely nauseated. Others it nearly killed, and in others it induced temporary insanity and numbness. Why? How? No one knows. It caused a considerable stir in the area, with families in such fear of being the phantom's next victims that husbands would stand guard all night with shotguns, while wives stuffed rags in every possible nook and cranny to prevent anyone from spraying gas into the house. Citizens formed an armed posse to hunt the culprit down, and the local cop assigned to the case, Officer Lemon (I picture him as Ed Wood's recurring policeman, Kelso) had his hands full trying to keep everyone from turning the county into the wild wild west.
The last of the Virginia incidents took place in February 1934, followed by the spate of Eustis/Umatilla/Mount Dora/Leesburg (Lake County) Florida incidents in May 1935. Of these Florida incidents we know little, but hopefully researchers will eventually glean more details from old newspapers not yet archived online. (Regular readers of my dribblings may note that Mount Dora is also where the fictional-yet-also-not Keyhole Vortex concept originates.)
Then, in 1944, it happened again. In August and September of that year, a man (or a woman dressed as a man) began pumping a weird toxic chemical gas into people's homes in Mattoon, Illinois. There were over a dozen cases spotlighted in the media, but there were also dozens more that were not reported in detail. So numerous were these reports of "the Mad Gasser of Mattoon" that police had to stop giving priority to them over other crimes.
The most famous Mattoon case was a Mrs. Kearney, who reported smelling a strong, sweet odor around 11:00 pm. The odor continued to increase in pungency and Mrs. Kearney began to lose feeling in her legs. Her sister, who has also in the house at the time, determined that it was coming from outside, through the open bedroom window. Then, after midnight, Mrs. Kearney's husband Bert returned home from a late-night shift at his job as a cab driver. He witnessed an unidentified man, very tall, dressed in black clothing and a black tight-fitting skullcap, crouching outside one of the house's windows. Kearney chased the man away but was unable to catch him. The story got national attention when TIME magazine picked it up.
Another Mattoon case worth noting: a woman named Beulah Cordes noticed a white handkerchief-lke cloth sitting on their porch by the screen door. She - rather foolishly - picked up the cloth and smelled it, which made her violently ill. She described the effect as being similar to an electric shock, and experienced a burning sensation in her mouth and throat. Soon her face began to swell and she vomited uncontrollably. As with other " Mad Gasser" victims, she also reported feeling weakness, dizziness, and partial paralysis of both her legs. Mrs. Cordes suggested that the chemical-sokaed cloth must have been left on the porch in order to knock out the family dog which usually slept there, so that the prowler could gain access to the house unnoticed.
In 2003, Scott Maruna published The Mad Gasser of Mattoon: Dispelling the Hysteria, which posits that the Mad Gasser was a local alcoholic named Farley Llewellyn who had a history of mental illness but was also a genius at chemistry. I remain unconvinced, but you can read Maruna's book or check out a Fortean Times article here that breaks it all down nicely in a nutshell.
The problem with the Farley Llewellyn theory, of course, is that it doesn't explain the identical cases in Virginia over a year earlier, nor is it inclusive of the similar and possibly related cases in Lake County, Florida. Conspiracy theories about the mystery sprayer abound to this day, involving everyone from the Nazis to aliens, as if either would be commonly found in a small Illinois town. Dr. Donald M. Johnson, in the 1954 issue of the Journal of Abnormal and Social Psychology, dismissed the whole thing as "mass hysteria", much in the same way smug skeptics would do a decade later during the "Windshield Pox" flap. But in so doing, Johnson proferred a lovely Lovecraftian description of the phantom anesthetist: "a shadowy manifestation of some unimaginable unknown." I like that.