Which particular people? Was it like military people under orders from European leaders? Maybe someone could help me understand -- with such a prolific practic

Which particular people? Was it like military people under orders from European leaders? Maybe someone could help me understand -- with such a prolific practice it must have been diaried and such? What are the best primary/secondary sources detailing the practice. I've heard the "they gave blankets but they knew the blankets had smallpox infection". But we presumably know who the they were. Presumably a lot of the colonists were sick as well. But not sick enough that the indigenous population noticed and stayed away. I guess people's capacity for evil is always greater than one can imagine.