A Traitor in Their Midst

[justcarol67]

No: HPFGUIDX 86078

Can anyone direct me to the interview in which JKR suggests that Harry
or his side will be betrayed by someone Harry trusts? I did a search
for both "traitor" and "betrayal" using the interview search engine
and came up with nothing. 

Two related questions:

1)Is that interview the source of all the ESE! speculation? If not,
what (aside from an incurable impulse to theorize) is that train of
thought all about? and 

2) Why does the traitor have to be a member of the Order? I really
don't buy Dumbledore, McGonagall, Lupin, Snape, or Bill as ESE. Why
not a member of Dumbledore's Army, if not (ugh) Cho, how about a
Gryffindor? My candidate of the moment is Seamus, who believed the
lies about Harry in the Daily Prophet. He would make a nice parallel
to Peter Pettigrew, a trusted roommate who drifted to the wrong side
through weakness. (Then again, his dad's a muggle, which would make
his family, and Dean Thomas's, candidates for extermination by the
DEs.) Or maybe Parvati Patil and Lavender Brown?

Reactions or suggestions, anybody?

Carol