"They (the activists) were committed to kill and be killed," retired Israeli general Giora Eiland told the BBC's Panorama television programme.
Eiland led an inquiry into the Israeli raid on the Mavi Marmara ferry on May 31, which left nine Turks, including a Turkish-American citizen, dead and dozens of others injured, including nine Israeli commandos.
The raid in international waters provoked a global backlash against Israel and led to the easing of a four-year blockade of the Hamas-ruled Gaza Strip.
Eiland said the resistance from the activists on the aid boat "was huge, much above expectation" and said it was surprising there were not more deaths.
"Under the circumstances in a very complex area like a ship, the results-the deaths-are surprisingly low," he told the BBC programme.
The military inquiry concluded last month that there were "professional mistakes regarding both the intelligence and the decision-making process" but said the commandos' use of live fire was justified.
Israel has set up another investigation into the raid, led by a retired Supreme Court judge, and the United Nations has also launch an inquiry.
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