I know nobody knows what they are thinking so I am wondering if it was ever discussed in and interview or anything like that
bulbapedia says the design is likely inspired by Koichi Zenigata from Lupin III http://en.wikipedia.org/wiki/Koichi_Zenigata
As Lupin III is far more popular in Japan, Looker and the Doctor wear completely different jackets, and the fact that Koichi is actually a detective, I'd have to agree with Bulba on this.