No - the difference between libel and slander is now a bit more complicated, not least due to modern media. If it's in permanent form (printed or broadcast, or part of public performance) it's libel, if it's spoken in a transient manner (day to day chat), it's slander. People do often still think of the radio as 'spoken' but in the law's eyes, it's a permanent record and thus on a par with a book.
Originally yes, it was much more 'written' vs 'spoken', but once people started recording the voice (tape, or video etc) it was effectively the same as printing something - i.e. many people could hear it over and over again. So nowadays, libel includes broadcasts and much more widespread than slander.
On the actual words - they probably said something like 'arrested for murder' which I think anybody would interpret as 'on suspicion of murder'. They'd only really be in trouble if they said he was guilty of it, and even then I doubt much would come of it if it was a one off mistake.