Richard Goldstone said his four member team had been shaken by the extent of the destruction in Gaza.
Witnesses from Gaza, Israel and the West Bank gave testimony in public hearings in Gaza and Geneva.
Israel has refused to co-operate, accusing the UN Human Rights Council of bias against it.
The investigation is looking into whether Israel and Hamas committed war crimes during Israel’s three-week operation in Gaza in December and January.
The Human Rights Council has been accused of singling out Israel unfairly, although Mr Goldstone, who is Jewish, is a respected South African war crimes prosecutor.