If Durham is saying there was nothing there, why was a criminal investigation opened in October ?

[Imperialism Inc.]

9. I hadn't read any more details past the day the story broke on CNN.

https://www.cnn.com/2019/11/21/politics/fbi-fisa-russia-investigation/index.html

A former FBI lawyer is under criminal investigation after allegedly altering a document related to 2016 surveillance of a Trump campaign adviser, several people briefed on the matter told CNN.

...
Horowitz turned over evidence on the allegedly altered document to John Durham, the federal prosecutor appointed early this year by Attorney General William Barr to conduct a broad investigation of intelligence gathered for the Russia probe by the CIA and other agencies, including the FBI. The altered document is also at least one focus of Durham's criminal probe.

It's unknown how significant a role the altered document played in the FBI's investigation of Page. The alterations were significant enough to have shifted the document's meaning and came up during a part of Horowitz's FISA review where details were classified, according to the sources. It did not change Horowitz's finding that the FISA application had a legal basis, The Washington Post first reported.