From National Post:

The “militarization” of urban police forces across the U.S., as well as in major Canadian cities, is a symptom of a decades-long arms race between criminals and the cops that’s been going on since the days of gangsters and Tommy guns, said Arthur Rizer, a former police officer and military lieutenant-colonel who now works at R Street Institute, a Washington think tank.

Modern police officers are well aware of the effect their methods, appearance and equipment have on public attitudes, said Rizer, who has spent the last several years surveying his former colleagues and researching their attitudes towards the evolution of their jobs and tactics.

“They know that it scares the public, and they’re OK with it,” he said.