The majority of the evidence supports the conclusion that Oswald acted alone (& this has seemingly been confirmed by analyzing the ballistics & cross-checking them with the layout of the vehicle that JFK was in).
Yes, the case against Oswald may be largely circumstantial (meaning no one actually witnessed him fire the shots), but that being said, the circumstantial case is fairly strong & includes the facts that he ordered the murder weapon by mail, worked at the building from which the shots were fired, left a palm print on the murder weapon, is believed to have murdered a police officer in the hours immediately after the assassination, & attempted to murder another police officer while he was being arrested. Such being the case - combined with his background as a troubled, depressed individual - leads to the likely conclusion that he was indeed the sole assassin.
Did he have any support leading up to the assassination? Who knows? He could very well have, but it doesn't seem necessary. All he needed was to be a good shot. I'll fully admit that anything is possible, but I'm just occam's razor-ing it here, & I'm not gonna make any further judgments until I see actual evidence instead of mere conspiracy theories.