*Spoilers* The Torture Victims

[Hannibal]

Are these just random people that the baron just took? Or were these actual criminals?

In a flashback, a man Daniel was about to torture claimed the murder was an accident, and in another we hear Daniel complain that they usually say it was an accident or it wasn't their fault--so at least some of those he tortured were involved in a crime. Whether they were convicted is unknown.

On the other hand, we know his victims at the dairy farm were totally innocent. That's what broke him.

In-between, we can't be too certain. Daniel wouldn't knowingly kill an innocent, but he also wasn't asking so many questions, and Alexander did collect innocents and was capable of lying.

But these are the four that Daniel personally tortured to death?

I strongly suspect there were more. First he's hesitant, then he goes through an improving stage where he's concerned the wheel will kill too quickly, and finally he's got it down to a thought-free science: "Paint & cut, paint & cut...". In my estimation that progression would take more than four kills.