Apart from multiple eye witnesses and multiple Oswald signatures.
And multiple documents - two from Oswald himself - stating it.
After he returned from MC, he mailed a typewritten letter to the Soviet Embassy in Washington discussing the visit (he complained about his treatment by the Cubans) and asking them to expedite his visa request. It was typed on Ruth Paine's typewriter (verified by the FBI). Both Ruth and Marina testified they saw him typing it. He had written out a rough draft - found by Ruth Paine - of that letter (below). The draft letter was in his handwriting. The typed letter was signed by him. The address on the label was identified as being written by him.
Witnesses on the bus going and returning, witnesses in MC, signatures, documents, photos for his transit visa application, circumstantial evidence....it's a pretty long list. I'm not sure what more is needed. Cuban and Soviet officials/personnel, including three KGB agents, said the man they met was Oswald. Were they in on it too? The CIA-KGB-Cuban intelligence conspiracy to frame Oswald? Whew, everybody was out to setup poor Oswald. The guy couldn't catch a break.
I keep repeating this in the hope that it'll get through. A triumph of hope over experience <g>.