It seems everyone is speculating that SN was used. But perhaps it was SA? (Sodium Azide). I don't know, of course, just my 2 cents.
SA is an odorless, tasteless, water-soluble crystalline powder. Exposure can cause rapid breathing and heart rate, low blood pressure, loss of consciousness, and respiratory failure leading to death.
SA causes dizziness, tachycardia, and fainting within seconds after ingestion. Symptoms, including decreased mental status, dizziness, fainting, tingling, hypotension, and fainting, develop minutes after consuming SA. Acute toxicity following exposure to SA is manifested by nausea, vomiting (as mentioned in the article), headache, reduced blood pressure, tachycardia, cardiac muscle ischemia, and metabolic acidosis. The final stage of poisoning may be characterized by coma, bradycardia, convulsions, cardiorespiratory arrest, and, ultimately, death.
SA is primarily a mitochondrial toxin, which binds the electron transport chain, inhibiting oxidative phosphorylation. The resulting reduction in adenosine triphosphate (ATP) production, even in the presence of oxygen, results in metabolic failure. This mechanism of action is similar to that of cyanide, although SA causes more pronounced vasodilation due to the in vivo conversion of some azide to the vasodilator nitric oxide. Some reports suggest that azide lethality is due to enhanced excitatory transmission from nitric oxide in the central nervous system.
There is no specific antidote for SA intoxication. A total of 185 individual SA cases have been reported concluding a 100% success rate in suicide cases.