The were roach killers because they were pointed and could kill roaches in corners
I worked in uniform in NY State's prisons for 25 years. My first experience of seeing a cockroach was at Auburn Prison while I was searching an inmate's cell. Each cell had a high shelf on the back wall, and when I pulled a shoe box off to search what was in it, a crapload of roaches went skittering from the shelf. Made me jump a mile. That was around 1980 or 81.
The fumigator came to the prison once a month and sprayed the messhall kitchen, the school buildings, and the industry buildings where they made license plates and metal office furniture. One of the worst areas for cockroaches was the bakery where the inmates made bread every day. They would bake the bread and put it in steel boxes for the next day's breakfast. They'd also put the formed dough in heated boxes for it to rise, but that didn't mean the cockroaches didn't get access to the bread and dough. Back then, an inmate could take a loaf of bread back to his cell at the evening meal. One of the things about cockroaches is that if you step on a female, you can carry the eggs on your shoes, and end up bringing them home. Thankfully that problem never occurred for me during the 25 years I spent working in the State's prisons.