detective

A police officer tasked with collecting evidence and information in order to solve a crime; an investigator.

He worked as a detective with the agency for five years.

The detective kept them in view. He made his way casually along the inside of the shelter until he reached an open scuttle close to where the two men were standing talking. Eavesdropping was not a thing Larard would have practised from choice, but there were times when, in the public interest, he had to do it, and this was one of them.

A person employed to find information not otherwise available to the public.

[…] Sherlock Holmes remarked calmly. […] "Well, I have a trade of my own. I suppose I am the only one in the world. I'm a consulting detective, if you can understand what that is. Here in London we have lots of Government detectives and lots of private ones. When these fellows are at fault they come to me, and I manage to put them on the right scent. They lay all the evidence before me, and I am generally able, by the help of my knowledge of the history of crime, to set them straight. There is a strong family resemblance about misdeeds, and if you have all the details of a thousand at your finger ends, it is odd if you can't unravel the thousand and first.[…]"

Had they responded this way in France or America, this wouldn't have surprised me, but wasn't everyone in England supposed to be a detective? Wasn't every crime, no matter how complex, solved in a timely fashion by either a professional or a hobbyist? That's the impression you get from British books and TV shows. Sherlock Holmes, Miss Marple, Hetty Wainthropp, Inspector George Gently: they come from every class and corner of the country. There’s even Edith Pargeter's Brother Cadfael, a Benedictine monk who solved crimes in twelfth-century Shrewsbury. No surveillance cameras, no fingerprints, not even a telephone, and still he cracked every case that came his way.

Employed in detecting.