Fine.
Then let's do the next best thing.
The US - or any Arab nation - should buy sophisticated equipment for forensics analysis of bullets and donate it to the cash-strapped PA.
Such as this:
Forensic Technology offers the world’s most advanced ballistic identification solution, IBIS® (Integrated Ballistic Identification System), which enables the sharing and comparison of significant quantities of exhibit information and images across a network of imaging sites, as well as the automated identification of likely matching bullets or cartridge cases. The latest generation of IBIS technology includes exceptional 3D imaging, advanced comparison algorithms, and a robust infrastructure. It has been designed to meet the needs of police and military organizations that gain actionable information from firearms and their fired ammunition components.
The Palestinian Authority can simply use this or another similar piece of equipment to create a high resolution 3D image of the bullet (or bullets, since there were more than one.)
At the same time, Israel can shoot test bullets from all the firearms they used in Jenin that day and take high resolution, 3D models of those.
Then anyone can see if they match and no one can easily lie.
Tampering would be impossible. Cheating would be difficult.
Yes, Israel could theoretically cheat - by not making available the weapon they said was the only possible one on their side. However, Israeli forensics is no doubt professional - meaning there is a documented, incorruptible chain of custody that can be examined by outsiders to ensure that everything is honest.
(And if you want an even playing field, then the Palestinian Authority security services should confiscate all the weapons in Jenin - which they should anyway! - and have them tested. Then things can be perfectly transparent!)
When it comes down to it, we know that the PA would not agree to this, even though it ostensibly addresses their concerns. Because everyone knows that the PA doesn't want anything that could possibly exonerate Israel. They are already getting the propaganda bonanza from their lies - why would they want to jeopardize that with a doze of transparent, provable truth?
But Israel should make the offer (the UAE or Bahrain could buy the equipment.) The PA's reasons for refusal will be absurd - and that is what the world needs to see.