I'd wondered whether he was THAT juror. I've been on a couple of juries and it seems there is always one that skirts the rules, doesn't pay close attention during the proceedings, and then is little invested in deliberations (is inclined toward one result, but states he can easily go either way depending on what everyone else wants). Likely never considers whether that is what he'd want were a jury of peers considering his fate.
Prosecutor Rachel Smith on Nate Eaton's Courtroom Insider last night described the process for how occurrences such as this are usually dealt with - defendant files a motion to have trial set aside, State and defense are both heard on the matter and some investigation/questioning may occur to determine whether the misconduct impacted the outcome, judge rules on the motion - either mistrial or the verdict stands. And if the verdict stands, it can be a later issue for appeal, although Ms. Smith said that the appellate court tends to give a lot of weight to the trial judge's ruling.
I fully expect that this verdict will stand. The jurors were all polled after the verdict was read and each stated their agreement with the verdict. This juror has stated conflicting claims in public in the chaotic atmosphere of reporters shouting questions at him as he exited the courthouse. Other jurors said that no one in the jury room knew about the other deaths and prior convictions when deliberating (so even if this one juror did, it doesn't sound like he used that information to influence others). Finally, the other jurors likely treated the proceedings and the deliberations - including their arguments presented to sway this juror's vote on the verdict - with much greater attention to their obligations than was displayed by this juror during proceedings and this judge observed that over the past few weeks and is going to give that some weight in his considerations.