I suspect you're arguing because you side with the juror, not because the logic is sound, and I have a problem with that, but let's stick with the facts.

But if he wasn't vetted out, it's nobody's fault except the lawyers'.

He perjured himself, as in, he lied, on purpose or otherwise. Lawyers aren't mind readers or psychics, you can't place complete blame on them because someone else commited a crime to get on the jury and they didn't catch it.

The system did exactly what it's designed to do, it mistrialed because a juror didn't follow the rules

The problem I have, and most people should have, is that because of one juror who didn't follow the rules we are extending the time, suffering, cost, and damages that shouldn't have happened.

They should have stricken him during the vetting process.

Yes! They should have, and because the juror SNUCK into the jury unfairly, it wasn't a fair trial.

He IS the problem. He started it. He made ALL of this worse. Not the lawyers, who could have done better, not the system, designed in the way that it is, not even the woman who murdered her children.

This is already an incredibly terrible thing, but people like the juror who lie to get what they want make it worse for everyone else.

Defending the person who commited a crime to make things worse because he wasn't caught early enough is just asinine.

But if he wasn’t vetted out, it’s nobody’s fault except the lawyers’.

This particular juror lied about his criminal history during jury selection. He shares culpability here.

I had to look this up because that in no way "ensures a free and fair trial"..the opposite is true

A jury is required to vote based strictly on the evidence. A juror can be removed for voting on a coin flip