Who: Xigbar, anyone who spots him
What: Prana collection
Where: Residential neighborhood, European-style section
When: Middle of the night
Warnings: I see dead people
Xigbar wasn't one to go out of his way to kill people when it didn't suit his purpose. He didn't get anything out of being cruel, this was just business. It saved his Master from having to supply more energy to him, which needed to be saved for other purposes, and it was more proactive than lounging around and watching the kid sleep. He wasn't quite sure how it worked, all that matters was that it did. Xigbar assumed it was something like spirits drawing in weaker ones, his essence consuming theirs as it left their mortal bodies.
It had been difficult choosing a hunting location, though. Hunting in the Japanese district was too close to home, someone might draw a connection. Of course, someone smart might think the opposite, that he was hunting in the other side of town to draw away suspicion from his home turf. It was convoluted to the point that even Xemnas would've given up working out the details of which location was better, so he just went with making sure the kid wasn't involved if someone found him and a fight broke out.
A single arrow-gunshot wound to the head was all it took. After a couple, the noise had roused the rest of the household and he'd had the pleasure of playing hide-and-seek with them. It didn't take long, they weren't very good at hiding, but the job was done. A family of four, dead in their homes, killed by an unusual weapon. Xigbar had seen the news reports of odd events happening locally, this would just be one more notch in the wood once discovered and go unsolved.
After all, it's hard to catch what you can't find. He dispelled the arrowguns; it was time to head back.