RAMd®d wrote:
1) Peremptory only works if they ask the right questions and there's usually a limit to the number they can do.

A peremptory ("no cause") challenge wouldn't be needed in a case like this.

Such a potential juror could be dismissed for cause, without using a peremptory challenge.

Someone could lie to get past the screening and voir dire, but there's no way the question of a law enforcement officer being a family member wasn't asked.

If either side discovered a potential juror was might be incapable of unbiased judgement, they could request they be dismissed 'for cause' without using one of their challenges.

Depending on the nature of a given court case, it could be that neither side might find a cop in the family a reason to dismiss.

Somewhere, somehow, some way, there have been or will be a situation where neither side asked such a question 'correctly' and somebody who did have a law enforcement member in the family, immediate or otherwise, told the truth as they new it and still got selected.

If that ever happens, you can say 'I called it'.

But don't hold your breath.