Polonium according to Chalk River Plant scientist... scientist said that

[applegrove]

whoever planned it wanted to be loud because it leaves a trail the way chemical poisons do not. Polonium is very heavy and unstable. It wants to spit out energy until is more stable. This type of radiation spits out alpha particle that are quite massive so easily stopped by layer of dead skin on your body (or paper or plastic). Hurts living tissue and the particles will blast away at your tissues if it ingested. You can find a single atom of radioactive material because of the radiation it emits. 130 day half life.

[Warpy]

1. Your friend is right

It's not something you can sneak out of a lab by the cupful. It's difficult to make, although it exists naturally in trace amounts.* One needs an advanced nuclear lab to produce enough of it to poison somebody.

Yes, this was a loud and clear to Russian expats who are critical of the Kremlin, especially those who know where some of the bodies are buried.


*Tobacco has an affinity for polonium uptake, one of the reasons it's deadly.