International law professor Julian Ku notes that, whereas both Israel and Palestine are accused of committing war crimes in the Gaza campaign, only Israel has any serious domestic mechanisms for investigating the allegations. Whereas Israel has launched an internal investigation on the practices of its military during the Gaza operation (encompassing, among other things, the shelling near a UN school and the usage of white phosphorus), Hamas spokespersons simply refused to investigate any allegations of human rights violations at all, saying they were "completely baseless and nonsense", stemming from the "Israeli propaganda machine of fabrication". This was in response to the allegation of using human shields -- though Hamas' rocket attacks on Israel are a per se war crime, Hamas refuses (I imagine) to concede that rule as legitimate in the first place.
Under international law, the international forums for the investigation and prosecution of war crimes in most cases are not supposed to be utilized unless the state in which the alleged crimes occurred is either unable or unwilling to investigate the allegations themselves through domestic processes. This is, in a large respect, a sop to the sovereignty of modern states, and runs into major problems when the alleged wrongdoer is an agent (or even just a national) of the state. An investigation by the Israeli government will undoubtedly not satisfy the Palestinians, nor will it necessarily be particularly credible given that in large part the judge is the same as the defendant. Still, Ku writes, "if it were subject to ICC jurisdiction, Israel would have a decent case for claiming to have fulfilled its duty to investigate and punish war crimes committed by its nationals or on its territory." By contrast, the blanket Palestinian denial and refusal to investigate would, potentially, be the sort of behavior which could trigger ICC jurisdiction.