Elon Musk countersued Twitter Inc on Friday, escalating his legal fight against the social media company over his bid to walk away from the US$44 billion purchase, although the lawsuit was filed confidentially. While the 164-page document was not publicly available, under court rules a redacted version could soon be made public. Musk’s lawsuit was filed hours after Chancellor Kathaleen McCormick of the Delaware Court of Chancery ordered a five-day trial beginning on October 17 to determine if Musk can walk away from the deal. Twitter did not immediately respond to a request for comment. Also on Friday, Musk was…