Interesting. The two juries are different. The 12 peers jury is from Anglo-Norman juree, past particple of jurer 'to swear' < Latin juro < jus (juris) 'law'. The temporary jury may be from ajurie 'help' < aider 'to help'. So, tha latter would be an example of word modified because of faulty morphological analysis, like (n)apron and (n)adder.