More than two years ago, in two separate episodes just four months apart, two men wielding knives in San Francisco were shot and killed by police officers. The killings spurred calls for police reform and eventually led to the resignation of the city’s police chief.

On Thursday, the San Francisco District Attorney’s Office, which investigated the episodes, announced that it would not bring criminal charges against the officers involved in either shooting.

Mario Woods, 26, was killed in December 2015. Luis Góngora Pat, 45, was killed in April 2016. In each case, the district attorney’s office determined, it was not unreasonable for the officers to have been in fear for their lives, or for the lives of others.

“Whether or not the officer could have used another tactic such as nonlethal force, or simply waiting, is not a factor we can even consider under current law,” District Attorney George Gascón said in a statement.