The prosecutor of the International Criminal Court has again refused to open an investigation into the deadly 2010 raid on a flotilla carrying aid to the besieged Gaza Strip.Appeals judges in September ordered Prosecutor Fatou Bensouda to reconsider her earlier refusals to open a formal investigation into the May 31, 2010, storming of the Mavi Marmara.Israeli commandos enforcing a naval blockade of the Gaza Strip killed eight Turkish citizens and one Turkish-American during the predawn raid the Mavi Marmara ship, which led a flotilla towards the besieged coastal enclave.More:New details on covert Israeli operation in Gaza revealedGaza's surviving al-Sawarka children struggle after Israel raidPalestinian teen shot dead by Israeli forces in Gaza StripSeveral other pro-Palestinian activists were wounded, while a 10th person died later of his wounds.Bensouda has acknowledged that war crimes may have been committed in the raid but decided that the case was not serious enough to merit an ICC probe.On Monday, she repeated that assertion."The Prosecutor maintains her view that there is not a reasonable basis to proceed, because there is no potential case arising from this situation that is sufficiently grave," Bensouda said in a 44-page document.This was because "there is no reasonable basis to conclude that any potential case arising from the situation would be of sufficient gravity to be admissible before the court," Bensouda said in a legal position she has taken before.'Not sufficiently grave'The order was the latest and likely the last step in a long legal battle to bring the case before the court.Bensouda first declined a request to investigate the raid in 2014. A panel of pretrial judges asked her to reconsider and she again refused to open an investigation in 2017. That decision was appealed, leading to the order in September to again reconsider.At the time, international lawyer Diala Chehade had told Al Jazeera that the concept of gravity within the text of the ICC has not been defined clearly enough in legal terms."There are currently no criteria that would set a final definition for the element of gravity for the ICC," said Chehade, who is also the former legal outreach officer for the Arab region at the court. The original request was made by the tiny Indian Ocean islands nation of Comoros because the Mavi Marmara was sailing under a Comoros flag.The ICC was set up as a court of last resort intended to prosecute senior leaders allegedly responsible for grave crimes including genocide, war crimes and crimes against humanity when national courts prove unable or unwilling to take on such cases.Israel is not a member state of the court but its nationals could have faced charges if Bensouda had opened an investigation.Separately, Bensouda's prosecution office is weighing up whether to open a formal investigation in the Palestinian territories, including Israel's illegal settlement policy, crimes allegedly committed by both sides in the 2014 assault on Gaza.Bensouda, who is stepping down as prosecutor in 2021, has yet to move to the next stage and open a full-blown investigation which could possibly lead to charges being brought.