If you think you can introduce reasonable doubt that someone got your ID and password and made the incriminating or inflammable posts or the posts that suggest you have a reckless and cavalier attitude towards the use of deadly force, there are other things you must take into consideration.
Considering, exclusively, use of deadly force where a criminal prosecution is probable, and there is cause sufficient to seize computers and access records... yes, this is probably true.
In other situations, maybe yes, maybe no.
For instance, I know (anecdotally) of a case wherein a law enforcement officer in a very, very small department and jurisdiction made pretty sweeping and inflammatory statements online regarding persons accused of sexually abusing children. That same officer was subsequently involved in a use of force (not fatal) involving a suspect accused of sexually abusing a child. It was alleged that the officer's conduct was excessive. The subsequent investigations (by IA and a private investigator acting on behalf of the suspect) revealed that the officer may have been posting online under an alias. The information was provided by one of the officer's extended family members who was a convicted sex offender. During a deposition, the officer acknowledged authorship of the posts despite the fact that there was insufficient cause to seize computers or subpoena ISP records. The department was subsequently sued, successfully. He could have simply denied authorship and, from a position of liability, the situation would have likely died. He would, however, have been finished in terms of his credibility with his department and the Court.
And, as I noted earlier, I know (personally) of an officer in a very large urban department whose investigation was attacked based upon the opinions he expressed online. Again, these were done under an alias and from a publicly accessible computer, but information was received that suggested that the officer was the author. It was obvious from the content that the posts were the officer's, but there was no way for the defense to prove it conclusively. Search warrants and seizures were not an option available to the defense. The officer COULD probably have denied authorship successfully, but to do so would have severely damaged his future credibility. He opted not to.
It really depends on the circumstances and severity of the situation. I agree that, if you are posting from your own account, and from your own computer, you will have a very hard time convincing a jury (or anyone else) that you are not responsible for the views expressed.
Insofar as writing style, etc is concerned, I am going to suggest, from the perspective of someone who has tried very, very hard to convince a number of DA's to introduce grammatical hallmarks in letters, emails, etc. as evidence in criminal prosecutions, that there is profoundly little likelihood that such evidence could be used in any way other than to support other evidence. Grammar, sentence structure, etc. might be enough to convince the mods at THR to ban someone, but in a criminal proceeding, where the defense is likely to present to the jury an expert who will juxtapose five indistinguishable posts from five different authors, there had better be something a great deal meatier. I would defy virtually anyone to distinguish my writing from that of my sister, or my wife of 18 years, based solely upon grammar, sentence structure, etc.
All that said, where "admissibility" is concerned, bet on it that if anyone has any inkling that you have posted something relevant to a Court proceeding, that information is likely to make it on the record regardless of whether or not it can be proven.
