The news media reports, in many cases such as the CT shooting, what is told to them by sources. When a spokesperson from the police tells them information, they do not know it to be true. In many cases, they cannot even begin to verify if it is true or not because they are not allowed inside the crime scene, so they report what is told to them.
NBC didn't admit to anything. They reported what was being told at the time it was being told. What is in that link was the information reported by the POLICE to reporters at the time that changed. It was also reported that the shooter was somebody else. There was no conspiracy there at all. The name given was provided by the police, but turned out to be wrong.
"If you look through your scope and see your shoe, aim higher."
-- said to me by my 11 year old daughter before going out for hogs 8/13/2011