“It’s not a time for I’m sorry, it’s time to put these bastards in jail.”

Severity against those bastards is charity towards the victims as well as towards future victims.

Leniency towards those bastards is murderous complicity towards future victims, because if the bastards are not punished hard, then a new wave of bastards will take the relay, and the mass poisoning will never end.

If I may recall a law dating from the Middle Age: The poisoners were condemned to death by been plunged into boiling water. Here is the explanation of the origin of this law:
A cook in a mansion, for some reasons, decided to “play a joke” by putting laxative in the meal he was preparing for the occasion of a big diner. The laxative happen to be a poison. Everyone, but one who was fasting, died.
The cook was condemned to be boiled to death by the tribunal of the town. The sentence was executed promptly on the main public place during the crowded market hour. This is how the execution took place: the condemned was suspended by his two ankles and his two fists backward so that he faced a large cauldron of boiling water into which he was slowly lowered. He was let in the boiling water long enough that he remained conscious, and then he was pulled pulled back, to be plunged again and again. It is reported that the poisoner cook was roaring in pain so loud that women in the crowd passed-out.
This kind of sentence, it televised live, would chill-out the bastards of the bio-weapon, and no one would try that trick again. Warranty.