My memory fails me, & my Google-Fu has fizzled.
During World War One, the US created an essentially all-amateur security & counterintelligence force that was 100% Civilian, & utterly useless. Bully-boys, who wound up abusing people with German last names. What was the name of this organization?
After World War One, a German spy, who operated in the US wrote a tell-all titled “Dark SOMETHING-OR-OTHER”. I cannot recall the “something-or-other”, nor the Author’s name.
To your second, it’s:
The Dark Invader
It wasn’t civilian, but could you be thinking of the Corps of Intelligence Police?
The American Protective League.
My thanks.
No, but thanks.
Bingo.
Much thanks!
NYPD Detective Tom Tunney’s bomb squad did some good anti-espionage work during WWI.
Their most famous exploit came when a squad member was tailing German commercial attache Heinrich Albert, who was involved in financing sabotage using a $30 million slush fund. Albert fell asleep while riding the subway one day, and almost missed his stop, jumping up and out of the car but forgetting his briefcase, which the tailing agent stole and got away with after a fruitless pursuit by Albert. Documents from the briefcase which revealed an astonishing level of German espionage against the U.S. got widely publicized, and the hapless Albert became known as the “minister without portfolio”. 
It’s one of the stories told in Howard Blum’s book about German spying and sabotage efforts against the U.S. in WWI, “Dark Invasion”.
Just don’t get confused like I once did and mix up Howard Blum and Howard Bloom.
Hey, I’m just glad I was able to uncover the truth as a civilian amateur who gets badmouthed by his German-last-named ex.