A number of these large flies were praying on smaller stuff / mid day / in the low altitude rainforest sections of SE Brazilian Rainforest
Here is a photo of Promachus rufipes (from North America) for comparison:
Coincidentally, even the prey (a wasp) is in the same position of the one in your photo!
This Genus has 9 species. If this is in fact Promachus, you'll have to find out which are found in South America.