Without loss of time, then, one of them, having carefully fashioned a strong loop of raw hide at the end of a long pole, and having dexterously slipped off his bast shirt, creeps slowly through the shallow water, pole and sling in hand, as near as possible to the alligator, which looks on at these preparations with perfect apathy, only now and then betraying a sign of life by a lazy movement of of its powerful tail. But it does not take its eyes off the Indian as he crawls nearer and nearer. The fatal sling is at arm's length from its muzzle, and yet it does not see it. As if under the influence of witchcraft, it continues to stare with its large protruding eyes at the bold hunter, who in the next moment has thrown the loop over its head, and suddenly drawn it to with a strong pull. The other Indians, who the while have been cowering motionless on shore, now rush into the water to the help of their companion, and four or five of them land the ugly creature that with all its might struggles to get back into the water, lashing the sand with its tail and showing its long teeth; but a few vigorous blows with an axe on the tail and skull soon render it tame enough....I never thought of sending a rifle-bullet through the thick skull of one, except on one occasion, when I was afraid that one of our Canichanas was about to make too close an acquaintance with the hard, jagged tail of an extraordinarily strong monster, which measured full 16 1/2 feet.
This quote is from page 90 of "Amazon and Madeira Rivers: Sketches and Descriptions from the Note-Book of an Explorer" by Franz Keller Leuzinger, published in 1875, and describes hunting caimans on the Madeira River, into which the rivers of the Llanos de Mojos flow. The book was once almost impossible to find, but was first reprinted by the Cornell University Library Digital Collections, and then posted as an open access document. It's one of the best 19th century accounts of the upper Madeira river, including Mojos, and it is illustrated with astounding woodcuts.