I will offer a counter-example to this. I was an alternate for my local county's grand jury for a year. I was selected through the same voir dire process used to place me on a petit jury for a criminal trial years later. It was wholly random. AFAIK, I didn't end up in the jury pool because I knew a prosecutor or cop. Were "I know a guy who knows a guy" the selection criteria, I would have never ended up on the grand jury, as my father was personal friends with a local defense attorney; the question posed to me wouldn't have been if I hate cops, but whether I knew or was associated with anyone sharing the same name as my father.