The topic of 'Suspects' is central to the podcast episodes provided, as they each explore various suspects and theories proposed in connection with high-profile criminal cases.

For example, the D.B. Cooper hijacking episode examines several prominent suspects, such as Kenneth Christensen, Richard McCoy Jr., and Robert Rackstraw. Similarly, the Jack the Ripper episode delves into suspects like Francis Tumblety, Joseph Barnett, H.H. Holmes, and Aaron Kosminski. The Casefile True Crime episode also discusses potential suspects like the 'horrible man' and Robert Penny in the hairdresser murders case.

The focus on identifying, profiling, and analyzing suspects is a common thread across these true crime podcast episodes, highlighting the importance of this topic in criminal investigations and true crime storytelling.