Examples:
Negotiations - There are reports of hostage deals having been proposed by Hamas just days after their capture. There have been multiple opportunities to come to ceasefire agreements, which could also cover options such as requiring perpetrators of crimes be handed over to an authority to face legal proceedings, etc.
Force - Israel and its international allies have the resources to engage in far more precise, targeted military operations, as has recently been demonstrated. These tactics have been used when convenient. However, Gaza has just been destroyed.
The sex and age distributions of casualties is very close to the population distributions, indicating that it is likely that reasonable steps to mitigate civilian casualties have not been taken. That's backed up by analyses of airstrike targets, video footage of military operations, eyewitness accounts, etc.
Humanitarian workers, journalists and healthcare professionals have been threatened, detained and killed.
There is evidence of aid being withheld, of 'evacuation information' being confusing or inaccurate.
There is evidence of torture and of military personnel expressing a desire and intention to kill every Palestinian, including children.