For two years, the mystery has endured: who set out to undercut climate scientists by publishing more than 1,000 of their private e-mails on the Internet?

The original e-mails, released in 2009 on the eve of a high-stakes United Nations climate conference in Copenhagen, sowed doubts about the scientists’ research and integrity and galvanized skeptics who challenge the scientific consensus that global warming is under way. It set off six separate official inquiries, all of which cleared the researchers of scientific misconduct.

Then the controversy receded. Yet recently, speculation about the identity of the person who leaked the messages has surged with the release of new e-mails and signs that a police inquiry is under way in Britain.

In November, just before another major international climate conference opened, this time in Durban, South Africa, another round of e-mails between the scientists were distributed online. Like those released in 2009, they were part of a trove taken from a computer server at the Climate Research Unit of the University of East Anglia in England; as before, the e-mail hijacker alerted the public to the e-mails in comments posted on various blogs.