Dissections/autopsies often were- And to some extent still are- A public spectacle with an audience, possibly a paying one. Apart from being invaluable for learning anatomy. They were often done with executed criminals.

Let's say that later the executions and dissections were combined; The criminal would be killed in front of the audience and immediately taken apart, maybe quickly enough for the heart to still beat after removal(depending on killing method). Certainly enough for there to be no rot; The events could be advertised as featuring no decay or (smelly, poisonous)preservatives, making them more attractive than other dissections. The convicts might be drugged to not upset the audience, and their body could be displayed, examined and explained before they are killed. Attractive women would naturally draw the largest crowds; Eventually the organizers started paying poor people or their parents so they can come, be killed and be cut. Often they would not need to be drugged, as it was expected of them to cooperate as was the deal. Later, people who defaulted on debts might be ordered by the court to do this, or this could be an explicit cause in the loan that they agreed to but hoped they could avoid. Maybe eventually some people sign up for this voluntarily, for reasons other than money for their family.