Mitchell

Andrew Mitchell was the British envoy to Prussia during the Seven Years' War. He spent a lot of time with Friedrich on campaign, and they were friends. He was not present for the events of 1730. In his memoirs, he recorded a brief sentence in which Friedrich commented on the execution.

That during his imprisonment at [Custrin] he had been treated in the harshest manner; brought to the window to see [Katt] beheaded; that he fainted away.

See selenak's write-up for more context on the memoirs and why we consider them a basically reliable source.

Thiebault

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Münchow

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von Johnn

August Friedrich von Johnn was the Danish envoy to Prussia in 1730. He was in Berlin when the execution was taking place at Küstrin. On November 11, 1730, he wrote an account of the execution in his formal report back to Denmark. This report, translated into German, was published in 1803 in Neue Berlinische Monatsschrift, vol. 9, pp. 342-344. The translation into English is mine.

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1731 pamphlet

The following anonymous pamphlet was published in Cologne in 1731. The copy used is this one from Google Books. It contains a two-page summary of events, followed by Katte's last letters to his stepmother, the King, his grandfather, and his father.

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