The number of U.S. law enforcement officers killed in action dropped sharply last year, a trend that policing experts said reflected the increased use of body armor by police.

In 2012, 48 law enforcement officers were killed on duty, down from 72 in 2011, according to Federal Bureau of Investigation figures released on Monday. Some 90 percent of those deaths involved firearms, statistics show.

“There’s been a sea change in the thinking on body armor” at the state and federal level, said Chuck Wexler, executive director of the Police Executive Research Forum.

In 2011, the U.S. Department of Justice began mandating the use of body armor for police departments that received certain federal grants. By late last year, 92 percent of federal law enforcement departments said they required officers to wear armor, according to surveys by the department.

In 2009, that had been the case in just 59 percent of those departments.

“In this case, policy made a difference,” Wexler said.

Accidents, especially car crashes, were the second leading cause of death. In 2012, 47 officers died in accidents, down from 53 in 2011.