Underage magic?

[Sharon]

Mecki:

> When Tom murdered his parents, he was supposed to have been 16 
years 
> old, right?
> now, the ministry can detect underage magic, Harry has experienced 
> that numerous times, then why was Morfin accused of the murder? I 
> mean, I realise he confessed as soon as he was asked, but why did 
> they suspect a grown man?
>


The Ministry cannot detect underage magic.  It never could.  
Dumbledore explains it best:

"[The Ministry] can detect magic, but not the perpetrator: you will 
remember that you were blamed by the Ministry for the Hover Charm 
that was, in fact, cast by -"

"Dobby," growled Harry; this injustice still rankled.  "So if you're 
underage and you do magic inside an adult witch or wizard's house, 
the Ministry won't know?"

"They will certainly be unable to tell who performed the magic," said 
Dumbledore, smiling slightly at the look of great indignation on 
Harry's face.  "They rely on witch and wizard parents to enforce 
their offspring's obedience while within their walls."

...HBP, pg 368, American edition (midway through Chp 17)

So there you have it.  The reason the Ministry whapped Harry in CoS 
is because they detected magic at Privet Drive; knowing that Harry is 
the only magical creature in that house, they naturally assumed that 
he had done it.  And when he claimed it was a house elf - well, why 
should they believe him?  A house elf in a Muggle household?  Don't 
be silly.

As for Morfin and the Riddles; the Ministry detected the magic done 
to kill the Riddles.  It did not know who had done the act because it 
can only detect magic, not the person who performs it.

--Sharon