Creating a hit lady for my novel

I created a professional hit lady by the name of Charlene "Charlie" Marx in my new novel, which is still under construction and still unnamed.

Before I gave Charlie life, I tried to do some research on hit ladies and serial killers. But there is not much information out there on hit ladies because they are relatively rare. Not many studies or research compiled on hit ladies or serial killers.

Most of what I could find on cold-blooded, ruthless killers reveals that they are almost always men. That makes it tough to develop my female character. She has a military background and combat training, but never actually experienced real warfare (the story is set in 1999 and women were serving in war zones, but not actually on the front lines).

But what actually makes Charlie tick, or more precisely, what in her background shaped her mentality so that she could kill for money without feeling or remorse?

Need is not enough. I'm going with a tortured childhood as the driving force that made her who she is. Charlie doesn't want to have children because of what she experienced. She was a foster child who was passed around from one set of abusive and uncaring parents to another. Adults who only took her to get  a check from the state. Time after time, she was used and abused.

It made Charlie hard. It made Charlie tough. And, when her youthful experiences were combined with what she learned in the military, it made her lethal.

Charlene's first kill was accidental. It amazed her that the death did not bother her in the least. In fact, seeing the body on the ground and lifeless at her hand actually gave her a thrill. That's when Charlene became Charlie and started a life of contract killing for a living.