### Instruction:
Where did Waldo E. Koop work?

### Input:
As a career, Waldo E. Koop was an engineer for Boeing. He was called one of the nation's finest researchers by local and state historians, and was credited in the series of Time Life books on the Old West for his research on gunfighters. Koop discovered that Henry McCarty, later known as Billy the Kid, spent time in Wichita, Kansas, where he saw his first gunfight. He published his findings in 1965 in the book, Billy the Kid: the Trail of a Kansas Legend.

### Response:
Waldo E. Koop was an engineer for Boeing before becoming one of the nation's finest researchers.