When did the "trace" come about?

[Carol]

No: HPFGUIDX 176254

zanooda wrote:
> 
> I  thought *around* really means around, close by :-). At least in
the same  house! Gaunt house and Riddle house were on two different
sides of town.  You are right that the Trace doesn't reveal the
identitiy of a person, but  shouldn't it show that the person is
underage? In Riddles case, the Trace  should have shown that either
some teenager killed them, or that some  teenager was present (around)
when Morfin did it. Or maybe I still  understand it all wrong ... :-).
 
Melissa replied:  
> I'm not sure that the houses were in different parts of the village
however the Ministry might have figured that  a teenager wouldn't have
been able to manage an AK.  Fake!Moody in GOF tells the class that
they could all point their wands at him and say the words he doubts
he'd get so much as a  nosebleed.

Carol responds:

The houses are close by, in the same small village, Little Hangleton.
Morfin refers to the Riddle House as "the big house on the hill,"
IIRC. However, to me the key point is that no underage wizard is known
to *live* in Little Hangleton. Frank Bryce mentioned a pale,
dark-haired teenage boy to the Muggle police, but no such boy was
mentioned to the Aurors, who, in any case, had Morfin's confession to
the murders. The Aurors didn't know that the Muggle Riddles had a
wizard son or grandson, and it never occurred to them to check
further. They probably figured that some underage witch or wizard
happened to be nearby when the murders were committed and let it go at
that. Tom Riddle had Stunned his uncle, stolen his ring, murdered his
parents, and disappeared before the Aurors even arrived. (If they sent
an owl announcing their intended arrival, Morfin would have ignored
the message even if he was conscious and could read, which is
doubtful.) all evidence pointed to him, just as it did to Sirius Black
so many years later.

In contrast, Harry's underage magic was detected in his own
neighborhood, where he was the only known wizard. So by their
caclulations, Harry had to be the person performing the magic. (They
wouldn't have bought the house-elf story if he'd had a chance to tell it.)

Carol, filling the plot hole as best she can and not very troubled by it