One of the most famous eyewitness accounts comes from, Lieutenant Horace Lockwood Smith-Dorrien
“I set to work, and next day, whilst sitting in my wagon, I saw two Zulus hanging on my gallows and was accused by the Brigade Major, Clery (afterwards General Sir Francis Clery), of having given the order. I was exonerated, however, when it was found that it was a case of lynch law performed by incensed men, who were bitter at the loss of their comrades. Other incidents of the same sort occurred in the next few days before law and order were re-established.”
When he says my Gallows he is referring to the frame used to dry ox-hides, which had became an improvised gallows "for hanging Zulus who were supposed to have behaved treacherously" during the battle.