i would honestly look at other factors such as the fishes health/age to start with, amanos are not really equipped to take down healthy fish that can swim away/escape, but they will almost certainly be the first at the dinner table if a fish course was served to them
Amanos are not really equipped nor have the instinct to hunt, well really anything, but especially not actively swimming fish. They’re delicate and wary. Until you catch one in the act of attacking a fish, i would look for other causes of death, such as perhaps an illness that might have been introduced with the shrimp and the water they came in, or unrelated factors.
PNW_Medaka 
i would honestly look at other factors such as the fishes health/age to start with, amanos are not really equipped to take down healthy fish that can swim away/escape, but they will almost certainly be the first at the dinner table if a fish course was served to them
Any chance it’s a whisker shrimp? They’re known killers.
I have heard that some Amanos get a taste of “meat” and keep killing fish. Very uncommon, but not impossible.
I agree that the amanos wouldn’t be my top culprit. How many fish in total do you have in the tank?
Amanos are not really equipped nor have the instinct to hunt, well really anything, but especially not actively swimming fish. They’re delicate and wary. Until you catch one in the act of attacking a fish, i would look for other causes of death, such as perhaps an illness that might have been introduced with the shrimp and the water they came in, or unrelated factors.
When I got an amano shrimp it immediately chased down and killed 2 cherry shrimp and started to eat them.
I don’t know about fish but I would return the amano to be on the safe side if your water parameters are good.