Sgt. Frog Episode 54: Dial M for Maybe I Can Solve This Murder!
Episode 54 of 358 of Sgt. Frog, aired April 15, 2005, 25 minutes. Available with English subtitles and dub where released.
Episode summary
Thinking that he has great powers of deduction, Keroro decides to open up a detective agency. It doesn`t go well. And then... the return of Dororo! Source: crunchyroll