Adam Lanza's Western Connecticut State University student ID photo. (Western Connecticut State University via AP)

The investigation into Adam Lanza's Dec. 14, 2012, rampage in Newtown, Conn., is now closed. The official report issued today doesn't contain much we didn't already know. But it does conclusively put to rest one theory that has been circulating on the Internet ever since Lanza murdered 20 children and seven others.

In the days following the tragedy, speculation ran rampant that Lanza had used the controversial forum known as 4Chan to telegraph his intentions.

"On 12/12 an individual logged onto a website called and anonymously posted 'I’m going to kill myself on Friday and it will make the news. be watching at 9:00 am,'" according to a search warrant cited in the official report. "(Then) another anonymous individual asked 'Where at?' The first individual responded 'I live in Connecticut, that’s as much as I’ll say.'"

4chan is an anonymous message board that's been credited for producing many of the Web's most persistent memes. It's also drawn criticism for its role in cyberbullying, hosting pornography and generally participating in other, seedier aspects of Internet culture. From that message board, the rumor spread to the conspiracy theory Web site Infowars — and then to Britain's Daily Mail tabloid, which cited Infowars by name.

Self-appointed sleuths took the unidentified 4Chan post on Dec. 12 to be Lanza. Further digging soon appeared to expose the posts as digitally edited screenshots, but officials weren't willing to rule out the lead as false until they had looked into it.

Today, the report from the Connecticut chief state's attorney finally closed the book on the rumor, declaring that it was "immediately investigated by federal law enforcement and found to have no validity and no relation to Newtown."

State officials declined to comment for this story.

Law enforcement, it turns out, didn't miss a warning they could have done something about. It's a small comfort, but a comfort nonetheless. For the rest of us, meanwhile, the story is yet another disturbing reminder of how easily we can be fooled by the Internet.