i'm sarah koenig. >> sreenivasan: first released in october, "serial" is a spin- off of the public radio program "this american life." each week, the program's investigation of the case seems to unfold along with the viewer. the focus: the 1999 conviction of a high school senior, anan syed, who was charged with murder of his ex-girlfriend, hae min lee. "serial" host and creator sarah koenig, takes listeners through an extensive re-examination of the alibis, testimony, work of the defense attorney done back then asking whether syed really was guilty. >> what grabbed me about this story is that a friend of the family came to me and said, "we believe this guy is innocent. there are holes in this case. can you take a look? >> sreenivasan: its a huge hit in the world of podcasting, garnering five million downloads on itunes, far more than any other podcast in history. but the idea of a "serial" is as old as charles dickens who experienced wild success with "the pickwick papers" in the mid 1800's. >> it is also often the most >> sreenivasan: the notion of podcasting stories has gained steam in

. >> reporter: the global hit is about a true crime in woodlawn, sarah koenig is the host of the podcast> something doesn't make sense here in this case, and i don't know where the problem is, and so it really is just me trying to figure that out. >> reporter: koenig and the "serial" case are looking into the case of adnan ayed convicted of killing his girlfriend in january 19 and buries her body in lincoln park. he was convicted on the testimony of an aquatance, he said he was going to kill lee, bury her body. throughout the podcast we hear from sayedd. koenig and her colleagues talk to people police didn't talk to and going back to the crime scenes. >> we can visualize what's happening and park and security and the best eye and all the places that, you know, the events of the story. >> reporter: a witness told police sayed used a pay phone outside this security boulevard best buy right after the murder. koenig and her team spent a great deal of time trying to find out if there was a pay phone there. it's that kind of digging that listeners love. >> i think it's just the storytelling me