1948 and an assassination of UN mediator
During the ethnic cleansing of Palestine in early 1948 (often called "tahur" in official Israeli documents, meaning "purification"), the UN observers on the ground were mostly moot spectators to the forced expulsions and massacres.
But there was one exception.
Ilan Pappe, an Israeli historian writes:
"𝘊𝘰𝘶𝘯𝘵 𝘍𝘰𝘭𝘬𝘦 𝘉𝘦𝘳𝘯𝘢𝘥𝘰𝘵𝘵𝘦 𝘩𝘢𝘥 𝘢𝘳𝘳𝘪𝘷𝘦𝘥 𝘪𝘯 𝘗𝘢𝘭𝘦𝘴𝘵𝘪𝘯𝘦 𝘰𝘯 20 𝘔𝘢𝘺 𝘢𝘯𝘥 𝘴𝘵𝘢𝘺𝘦𝘥 𝘵𝘩𝘦𝘳𝘦 𝘶𝘯𝘵𝘪𝘭 𝘑𝘦𝘸𝘪𝘴𝘩 𝘵𝘦𝘳𝘳𝘰𝘳𝘪𝘴𝘵𝘴 𝘮𝘶𝘳𝘥𝘦𝘳𝘦𝘥 𝘩𝘪𝘮 𝘪𝘯 𝘚𝘦𝘱𝘵𝘦𝘮𝘣𝘦𝘳 𝘧𝘰𝘳 𝘩𝘢𝘷𝘪𝘯𝘨 ‘𝘥𝘢𝘳𝘦𝘥’ 𝘵𝘰 𝘱𝘶𝘵 𝘧𝘰𝘳𝘸𝘢𝘳𝘥 𝘢 𝘱𝘳𝘰𝘱𝘰𝘴𝘢𝘭 𝘵𝘰 𝘳𝘦-𝘥𝘪𝘷𝘪𝘥𝘦 𝘵𝘩𝘦 𝘤𝘰𝘶𝘯𝘵𝘳𝘺 𝘪𝘯 𝘩𝘢𝘭𝘧, 𝘢𝘯𝘥 𝘵𝘰 𝘥𝘦𝘮𝘢𝘯𝘥 𝘵𝘩𝘦 𝘶𝘯𝘤𝘰𝘯𝘥𝘪𝘵𝘪𝘰𝘯𝘢𝘭 𝘳𝘦𝘵𝘶𝘳𝘯 𝘰𝘧 𝘢𝘭𝘭 𝘵𝘩𝘦 𝘳𝘦𝘧𝘶𝘨𝘦𝘦𝘴.
𝘏𝘦 𝘩𝘢𝘥 𝘢𝘭𝘳𝘦𝘢𝘥𝘺 𝘤𝘢𝘭𝘭𝘦𝘥 𝘧𝘰𝘳 𝘵𝘩𝘦 𝘳𝘦𝘧𝘶𝘨𝘦𝘦𝘴’ 𝘳𝘦𝘱𝘢𝘵𝘳𝘪𝘢𝘵𝘪𝘰𝘯 𝘥𝘶𝘳𝘪𝘯𝘨 𝘵𝘩𝘦 𝘧𝘪𝘳𝘴𝘵 𝘵𝘳𝘶𝘤𝘦, 𝘸𝘩𝘪𝘤𝘩 𝘩𝘢𝘥 𝘣𝘦𝘦𝘯 𝘪𝘨𝘯𝘰𝘳𝘦𝘥, 𝘢𝘯𝘥 𝘸𝘩𝘦𝘯 𝘩𝘦 𝘳𝘦𝘱𝘦𝘢𝘵𝘦𝘥 𝘩𝘪𝘴 𝘳𝘦𝘤𝘰𝘮𝘮𝘦𝘯𝘥𝘢𝘵𝘪𝘰𝘯 𝘪𝘯 𝘵𝘩𝘦 𝘧𝘪𝘯𝘢𝘭 𝘳𝘦𝘱𝘰𝘳𝘵 𝘩𝘦 𝘴𝘶𝘣𝘮𝘪𝘵𝘵𝘦𝘥 𝘵𝘰 𝘵𝘩𝘦 𝘜𝘕, 𝘩𝘦 𝘸𝘢𝘴 𝘢𝘴𝘴𝘢𝘴𝘴𝘪𝘯𝘢𝘵𝘦𝘥.
𝘚𝘵𝘪𝘭𝘭, 𝘪𝘵 𝘪𝘴 𝘵𝘩𝘢𝘯𝘬𝘴 𝘵𝘰 𝘉𝘦𝘳𝘯𝘢𝘥𝘰𝘵𝘵𝘦 𝘵𝘩𝘢𝘵 𝘪𝘯 𝘋𝘦𝘤𝘦𝘮𝘣𝘦𝘳 1948, 𝘵𝘩𝘦 𝘜𝘕 𝘎𝘦𝘯𝘦𝘳𝘢𝘭 𝘈𝘴𝘴𝘦𝘮𝘣𝘭𝘺 𝘱𝘰𝘴𝘵𝘩𝘶𝘮𝘰𝘶𝘴𝘭𝘺 𝘢𝘥𝘰𝘱𝘵𝘦𝘥 𝘩𝘪𝘴 𝘭𝘦𝘨𝘢𝘤𝘺 𝘢𝘯𝘥 𝘳𝘦𝘤𝘰𝘮𝘮𝘦𝘯𝘥𝘦𝘥 𝘵𝘩𝘦 𝘶𝘯𝘲𝘶𝘢𝘭𝘪𝘧𝘪𝘦𝘥 𝘳𝘦𝘵𝘶𝘳𝘯 𝘰𝘧 𝘢𝘭𝘭 𝘵𝘩𝘦 𝘳𝘦𝘧𝘶𝘨𝘦𝘦𝘴 𝘐𝘴𝘳𝘢𝘦𝘭 𝘩𝘢𝘥 𝘦𝘹𝘱𝘦𝘭𝘭𝘦𝘥, 𝘰𝘯𝘦 𝘰𝘧 𝘢 𝘩𝘰𝘴𝘵 𝘰𝘧 𝘜𝘕 𝘳𝘦𝘴𝘰𝘭𝘶𝘵𝘪𝘰𝘯𝘴 𝘐𝘴𝘳𝘢𝘦𝘭 𝘩𝘢𝘴 𝘴𝘺𝘴𝘵𝘦𝘮𝘢𝘵𝘪𝘤𝘢𝘭𝘭𝘺 𝘪𝘨𝘯𝘰𝘳𝘦𝘥.
𝘈𝘴 𝘱𝘳𝘦𝘴𝘪𝘥𝘦𝘯𝘵 𝘰𝘧 𝘵𝘩𝘦 𝘚𝘸𝘦𝘥𝘪𝘴𝘩 𝘙𝘦𝘥 𝘊𝘳𝘰𝘴𝘴, 𝘉𝘦𝘳𝘯𝘢𝘥𝘰𝘵𝘵𝘦 𝘩𝘢𝘥 𝘣𝘦𝘦𝘯 𝘪𝘯𝘴𝘵𝘳𝘶𝘮𝘦𝘯𝘵𝘢𝘭 𝘪𝘯 𝘴𝘢𝘷𝘪𝘯𝘨 𝘑𝘦𝘸𝘴 𝘧𝘳𝘰𝘮 𝘵𝘩𝘦 𝘕𝘢𝘻𝘪𝘴 𝘥𝘶𝘳𝘪𝘯𝘨 𝘵𝘩𝘦 𝘚𝘦𝘤𝘰𝘯𝘥 𝘞𝘰𝘳𝘭𝘥 𝘞𝘢𝘳 𝘢𝘯𝘥 𝘵𝘩𝘪𝘴 𝘸𝘢𝘴 𝘸𝘩𝘺 𝘵𝘩𝘦 𝘐𝘴𝘳𝘢𝘦𝘭𝘪 𝘨𝘰𝘷𝘦𝘳𝘯𝘮𝘦𝘯𝘵 𝘩𝘢𝘥 𝘢𝘨𝘳𝘦𝘦𝘥 𝘵𝘰 𝘩𝘪𝘴 𝘢𝘱𝘱𝘰𝘪𝘯𝘵𝘮𝘦𝘯𝘵 𝘢𝘴 𝘢 𝘜𝘕 𝘮𝘦𝘥𝘪𝘢𝘵𝘰𝘳: 𝒕𝒉𝒆𝒚 𝒉𝒂𝒅 𝒏𝒐𝒕 𝒆𝒙𝒑𝒆𝒄𝒕𝒆𝒅 𝒉𝒊𝒎 𝒕𝒐 𝒕𝒓𝒚 𝒕𝒐 𝒅𝒐 𝒇𝒐𝒓 𝒕𝒉𝒆 𝑷𝒂𝒍𝒆𝒔𝒕𝒊𝒏𝒊𝒂𝒏𝒔 𝒘𝒉𝒂𝒕 𝒉𝒆 𝒉𝒂𝒅 𝒅𝒐𝒏𝒆 𝒇𝒐𝒓 𝒕𝒉𝒆 𝑱𝒆𝒘𝒔 𝒐𝒏𝒍𝒚 𝒂 𝒇𝒆𝒘 𝒚𝒆𝒂𝒓𝒔 𝒃𝒆𝒇𝒐𝒓𝒆"
His assassination was ordered by a 3-member team, which included Yitzhak Shamir, who would go onto become the Prime Minister of Israel. The actual killers were also widely known in but never brought to justice. Their group, "the Stern Gang", however, was disbanded after this incident.
(Quote taken from Illan Pappe's "The Ethnic Cleansing of Palestine")