A British police unit on Wednesday formally closed its criminal investigation into the unauthorized publication of thousands of sensitive scientific e-mails from the University of East Anglia’s climate change research institute, saying that it could not identify the hacker.

The investigation by the unit, the Norfolk Constabulary, into the data leak concluded that the hacking was a “sophisticated and carefully orchestrated attack” on the university’s digital data files by an unknown outsider operating remotely online. The police put to rest speculation that the release was the work of a mischievous or disgruntled insider at the university’s Climatic Research Unit.

The leak in November 2009 set off a battle over the integrity of some of the world’s leading climate scientists and their research. Some of the e-mails contained provocative language about those who question the prevailing scientific view that the global climate is heating up because of the burning of fossil fuels and other human activities.

Climate change doubters called the release Climategate and demanded an investigation into the academic honesty of the e-mails’ authors and their research. A half-dozen such inquiries, in Britain and the United States, largely cleared the scientists of wrongdoing, but in some cases chided the authors for an intemperate tone.