Thing is, any cunt can slaughter masses. If they don't have access to buyable automatic firearms, there are shrapnel-bombs, nerve agents, hell, if somebody so chose, mustard 'gas' (they aren't gases) could be prepared with a trip to a garden center, a DIY store and somewhere to get a car battery charger, if a jihadi wanted to do it from scratch. Or if you want to keep it simple, release a load of arsine gas (the arsenic answer to ammonia, AsH3, rather than NH3) by fusing arsenic with a metal, such as iron perhaps and creating the metal arsenide, and on exposure to acid, this would release the lethally toxic arsine. Stinks something heinous too, like rotting garlic/onion laced with whatever that smell is you get from holding copper coins in your hand for a while, or like rotting leeks mixed with a hint of rust.
Or hell, bet as much if not more damage would be done if a jihadi type were to target the infrastructure of a country, by setting off something like an explosively-pumped magnetic flux compression generator, and doing it close to power plants, using the resulting massive electromagnetic pulse to fry the circuitry of the power plants, and that would go tenfold for a nuclear power plant. Or even simpler, target the plant with a high-powered vircator (a vacuum-tube based microwave pulse generator, at max output and correct design, capable of terawatt-level output)
Country loses power after coordinated attacks of that kind and everything would devolve into mass panic.
And if the terrorists are set on stone-age primitive, just look at the truck attacks in the UK.
