Every person he killed is a unique thing within the world that will never return to it and that was valuable. Once that loses value then nearly everything does as well and you start to slip into the cold ways of evil wizards. It may not be immediate and may even take quite some time but eventually the "how" you obtain favorable results will start to matter less than the results themselves. It was one of the reasons Nick disliked Dumbledore so much as he was starting to care less about the "how" compared to the end results.-
This was how his "for the greater good" mindset worked and was unpleasant to say the least. Anyways Knockturn alley was a dark and dreary place with poorly maintained buildings that had various discolorations of their outside walls and rust on their metal signs. Contrary to what the books would have one believe Borgin and Burkes was not the biggest or most eye catching store in the alley. The truth was that it was merely the largest store that was near the entrance/exit of Knockturn alley. Nick didn't enter that particular store as he only felt a single interesting magical item in the store and it wasn't a creature part.-
It should be understood like moving about with a transfigured body was uncomfortable to say the least so Nick wanted nothing more than to complete his business in this place as fast as possible. While he walked deeper into the alley he felt someone approaching him from behind from his right side with their left hand stiff in front of them. 'A pickpocket huh , lets give him a bit of a scare.' Nick thought and casually tapped the tip of his wand on his robe the moment the person bumped into him.-
"Oh sorry abou … What the hell!?" the hooded man started before panicking when he realized he couldn't take his hand out of Nicks pocket , which was also empty by the way. Nick wasn't planning on killing the thief however as he had no magical taint from dark magic and thus likely wasn't that bad of a person , this was quite the accomplishment for someone in Knockturn alley. "Now what would a person that has never used dark magic be doing within this place?" Nick asked calmly while ignoring the mans repeated attempts to escape from his transfigured pocket.-
"What does it matter , you'll just kill me either way." the thief said bitterly once he figured out that it was impossible to escape. Nick smirked "How's about you and I make a deal? The terms are simple , You satisfy my curiosity and in exchange I will let you go without any injuries or messy surprises. Interested?" he asked like a demon making a tempting offer. "How do I know you will honor your end of the deal?" the man asked suspiciously. Nicks smirk grew wider "You don't exactly have much choice but to take my word for it do you?" he asked with a chuckle.-
The man ground his teeth angrily for a moment before speaking again "Fine! What do you want to know?" he asked in defeat. "First answer my original question then we will go from there." Nick said calmly. "I am a muggleborn wizard so when I received my Hogwarts letter my parents and I were rather surprised. I am not all that talented at magic if I'm being honest , barely average in fact. Anyways I was fascinated with magic despite this and after graduating I spent the next five years traveling around the world to see all the different magics of the world." He paused for a moment.-
Nick knew the plot twist must be coming up thanks to this pause as people tend to only stop when they need a moment to collect themselves mid speech. "Anyways about a year ago I met a what I thought was a wonderful woman that took my breath away in more than one way it turned out. In hindsight I should have known there was something wrong with the situation when she actually showed interest in me despite me not being very attractive."-
"As it turned out that woman was a vampire belonging to one of the clans that operated in Sweden and turned me in my sleep after I slept with her. Ever since then I have needed to turn to thievery just to afford the cost of blood in order to survive." The man finally finished his story and Nick actually pitied the poor guy. Vampires were cursed beings that while unaging pay a heavy price for it. First they must drink magical blood to sustain themselves which without hunting is obviously very pricey. Second is the agony they have upon any sunlight touching their skin which explained why the man was so well covered.