Don.
But they didn't find Palestinian fighters, who had already left.

There were reports of fighting. Exchanges of fire.
If there were none, they were still expected.
NYT states that IDF came under fire AFTER the PLO were supposed to have withdrawn.
The Phalange were sent in by IDF to clear the camps of fighters.

Re your demands for unequivocal evidence.
He who makes outrageous accusations should provide the unequivocal evidence, not demand it of someone asking why to believe it.