1) If they identify the twitter account and associate it to a person how can they prove he/she made the tweet? "I left my phone at the table at the bar and someone must have picked it up and tweeted something"
2) If they identify the computer used to make the tweet how can they identify the person who used that computer. "My GF and her friends were all playing around the computer that day"
If I were the person that made the tweet I wouldn't make any statements and I would have my lawyer press for proof that the tweet was in fact "by my hand"