Oswald was married to a Russian born girl whom he met while studying Russia. Jack Ruby was a fellow well known to Dallas Plice as a Crime "buff." His nightclub had many cops as patrons & he was so well knownto them, he was allowed entrance without being frisked.   

Beer, I think the one thing you can safely rule out is a religous motivation. Ruby was painted as a great admirer of JFK & Jackie. He was portrayed as being in great distress over the JFK's death & simply wanted revenge.

I've always thought a possible motive, among others, was that JFK wanted to disallow the oil depletion allowance. That made many Texans see Red. If you get enough people together, each with their own reason to arrange a murder, it's possible to kill a president & cover it up.