Did Lee Harvey Oswald act alone?

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I also agree this is one of the few conspiracy theories that make sense.

1.How was Oswald, if he did the shooting at all, able to get into the Soviet Union and then re-enter the United States with no problems not too long later?

2.How did the shooter get off the number of shots fired in the time given?

3.I don't think the forensic evidence points to Oswald.  The 'single bullet theory' is absolute nonsense.  And the author of that theory, Arlen Spector, is not a physicist.  

4.Why did Jack Ruby, a known Mafia member, kill Oswald?  The reason he gave also strikes me as absolute nonsense.

5.It wasn't known at the time, but it is now known that the CIA and the Mafia were working together to assassinate at least one foreign leader: Fidel Castro.  They may have collaborated on killing other foreign leaders, and if they collaborated on  attempting to kill at least one foreign leader, why couldn't they have killed a domestic leader whom they both hated?

I am aware that in seemingly every murder investigation (which is what this basically is) there are anomalies that could be made out to suggest conspiracy theories, but I do think in this case these anomalies point to a possibility, and maybe even a strong possibility, of CIA/Mafia involvement. 

Of course, I don't know if this was at the top of the CIA who wanted to stop Kennedy before he could 'break their agency into a million pieces' or just rogue elements who were unhappy with Kennedy's treatment of the Dulles brothers.