The incidents were the 2015 shooting of Mario Woods and the 2016 shooting of Luis Gongora.
Gascon said no crime was committed by police based on the current law, therefore his office could not charge the officers involved. "We do not bring charges against people who have not broken the law," Gascon said.
The announcement was made after Gascon met with Gongora's family. Woods' mother, Gwen, was also invited, but she was not present during that meeting.
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In a December 2, 2015 cellphone video, you can hear a woman yelling for 26-year-old Woods to put down the knife he was holding. Police said the knife had been used by Woods earlier against another man. Despite police shooting beanbag rounds at Woods, he never dropped it and police then fired 26 rounds.
Gascon said the use of force in that case was not only excessive, but unnecessary. However, under current law there was nothing he could do to charge those officers. "Under current law, police officers do not have to retreat, police officers don't have to use the minimum force necessary," he said.
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In that case, police argued that they feared for their safety and the public's well-being.
The same applied to this April 7, 2016 shooting, when witnesses say 45-year-old Gongora, holding a knife, confronted police. A home security video doesn't show the moment Gongora was shot, but you can see when police arrived and you can hear how it unfolded only 30 seconds later with police shooting and killing Gongora.
An anonymous viewer gave ABC7 News video that captured audio of the deadly encounter in San Francisco's Mission District.
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In the video, officers can clearly be heard ordering Gongora to put down the knife, before using the non-lethal rounds and then the lethal rounds.
Gongora was taken to San Francisco General Hospital, where he died from his injuries.
The shooting prompted wide-spread community outrage and put pressure on the police department which eventually led to the ousting of then San Francisco Police Chief Greg Suhr.
It also led the department to change officer training for officers to emphasize de-escalation tactics when dealing with suspects.
The Police Officer's Association say in both cases police acted within the department's rules and there was no excessive force. "I don't believe it was. The members were put in a situation where they felt they needed to not only defend themselves, but defend the public in the area," said Tony Montoya, the President of the San Francisco Police Officer's Association.
Gascon told reporters the current law needs reforming. He is now behind assembly bill 931 which would allow police to use lethal force only when necessary, not when it's reasonable. "As a society, we are failing some our most vulnerable communities when it comes to police use of force, " said Gascon.
Right after both incidents, the officers were placed on paid administrative leave fore 90 days. When they returned, they were put on desk duty pending the outcome of the DA's investigation.
Gascon: “Under the law no crime has been committed. Still, I am very disturbed, but must adhere to the law. “ The D. A. is referring to the shootings of Mario Woods and Luis Góngora. pic.twitter.com/s4pyE7wP6N— Lyanne Melendez (@LyanneMelendez) May 24, 2018