MEMPHIS, Tenn.—Surveillance cameras like the one that captured police officers beating Tyre Nichols have proliferated in the U.S. in recent years, even as researchers, civil-liberties advocates and law-enforcement officials debate whether they are effective at combating violent crime. Footage released last week by the city of Memphis from a pole-mounted surveillance camera provided a clearer view than the officers’ body-worn cameras of the Jan. 7 encounter, when Mr. Nichols was punched, kicked and struck with batons. He died in a Memphis hospital three days later.

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