Lawyers for Erickson Dimas-Martinez appealed against his murder conviction, arguing that the juror posted on the internet, despite the judge’s instruction not to.
They also complained that another juror was sleeping in the Arkansas court.
Juror Randy Franco tweeted: “Choices to be made. Hearts to be broken … We each define the great line”.
Under an hour before the jury announced its verdict, he tweeted: “It’s over.”
Dimas-Martinez, now 26, was convicted of robbing and shooting a teenager in north west Arkansas in 2006.
At the start of the case, the judge had said: “Just remember, never discuss this case over your cell phone … and don’t Twitter anybody about this case.”
Franco tweeted at other points in the trial too, saying: “The coffee sucks in here,” and “Court. Day 5. here we go again.”
Franco has defended his tweets, saying none of them divulged any details of the trial itself.
The judge said in the ruling: “Because of the very nature of Twitter as an online social media site, Juror 2’s tweets about the trial were very much public discussions.
“Even if such discussions were one-sided it is in no way appropriate for a juror to state musings, thoughts or other information about a case in such a public fashion.”
Dimas-Martinez will be retried at a later date.
The court said: “Because we conclude that the one juror sleeping and a second juror tweeting constituted juror misconduct, we reverse and remand for a new trial.”