Who is the person that deletes messages in the news group ?

No one. Messages on the newsgroups float around in CyberSpace forever. You can
pick up articles from the 1980's on Google.com, from the days when it was
refered to as usenet, the internet didn't exist and FidoNet was a big deal on a
lightning fast 9600 baud BBS.
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73! de Andy KC2SSB (ex: KF4KHC/HL9HCT)
Beachwood, NJ USA! Grid FM29vw
http://vhfradiobuff.tripod.com
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National "Do Not Call" Registry: http://donotcall.gov