When did the "trace" come about?

[zanooda2]

No: HPFGUIDX 176165

--- In HPforGrownups at yahoogroups.com, "Steve" <bboyminn at ...> wrote:

> I think it identifies location; that is, magic in 
> the vicinity of Harry. That explains why the Ministry
> thought Harry cast the Hover Charm, when it was really
> Dobby. Magic occurred in the vicinity of Harry, and
> since Harry is the only wizard in the vicinity, they
> conclude it had to be Harry.


But, if only underage wizards have the Trace on them, how come the 
Ministry didn't know that it couldn't be Morfin who killed the Riddles? 
I'm sure Morfin was older than seventeen. They should have known it was 
someone underage who committed the murders, not Morfin, right? Ah well, 
if JKR was ever asked about it, she'd probably say that the Trace was 
not yet invented when LV was underage ... :-).

zanooda, still confused about the Trace