Choosing the Proper Villain
Writing mysteries is an exercise in pitting bad characters against good.
There are degrees of bad and good, of course, but in compelling stories, the bad character is often seriously, diabolically, dangerously bad. He (or she) will certainly have good points. He may be charming, clever, handsome, sympathetic, and have superior interpersonal skills–think Ted Bundy–but the reader learns soon that these are just a cover, enabling him to get close to people in order to do his dirty work.
I have used individuals in my books to play the villain. An art critic, a factory owner, a southern sympathizer, a rich landowner. In others, I have used a group (or blast, or den, or herd, or flock, or conflagration—see my last blog on word play) of baddies, ie: Nazis, where most folk will agree that it’s easier to count the good ones than the bad.
A “collective” villain makes for an interesting read.
The Nazis, the hedge fund crooks, the greedy corporate thieves, the Republicans, the Democrats, the tax collectors, the CIA, the FBI, the police, lawyers, politicians, doctors . . . all can play the role of collective villains.
In the case of the Nazis, you expect evil. In the case of doctors, you may not.
Anyone can be a villain.
If your experience tells you Nazis are bad, a good Nazi will be an interesting character. Same is true in reverse for a doctor. Then you have the Nazi doctor and you won’t know what to believe. But I digress.
A good writer will build each character with good points and bad points that the reader will both admire and loathe. It’s a fine line to walk. If your reader loathes your character too much, he (or she) might put the book down. 
In the case of the Nazis, there is, built-in, a sense of evil, danger, and villainy. And because Nazis were historically real, readers will have an innate sense of foreboding right from the first page.
Hence, my next book will return to the Nazis and World War II. The theme will be not be confiscated art . . . but stolen music.