Speaking at the Rose Garden, Tretta spoke about the 2019 school shooting in the city of Santa Clarita that killed two of her classmates, including one of her best friends, Dominic Blackwell.
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"I was airlifted to the hospital and spent hours in surgery, having a bullet removed from my abdomen that was millimeters away from my major artery," she said. "Then my parents told me the terrible truth. Dominic had died, and so had another classmate, Gracie Anne Muehlberger, a 15-year-old girl who had an infectious laugh."
The 16-year-old suspect, who died a day later after he shot himself, used a ghost gun in the shooting.
"For reasons I will never know he had brought his father's weapon to school," Tretta said of the shooter. "A firearm I would come to know as a ghost gun."
RELATED: President Joe Biden aims at 'ghost gun' violence with new federal rule
Biden aims at 'ghost gun' violence with new federal rule
A ghost gun is a firearm that comes packaged in parts, can be bought online and assembled without much of a trace -- a point President Joe Biden demonstrated with props at the press conference announcing the regulations.
Tretta introduced Biden, whom she called "the strongest gun-sense commander in chief ever to hold office" to make his big announcement.
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"Starting today, weapons like the one used in Saugus High School and to ambush deputies that are here with us today are being treated like the deadly firearms they are," Biden said. "If you commit a crime with a ghost gun, expect federal prosecution."
"This rule is an important step, it's going to make a difference, I promise you," Biden added.
The new rule changes the current definition of a firearm under federal law to include unfinished parts, like the frame of a handgun or the receiver of a long gun. It says those parts must be licensed and include serial numbers. Manufacturers must also run background checks before a sale - as they do with other commercially made firearms. The requirement applies regardless of how the firearm was made, meaning it includes ghost guns made from individual parts, kits, or by 3D-printers.
Federally licensed firearms dealers must retain key records until they shut down their business or licensed activity and then transfer the records to ATF as they are currently required to do at the end of licensed activity. Previously, these dealers were permitted to destroy most records after 20 years, making it harder for law enforcement to trace firearms found at crime scenes.
"A year ago this week standing here with many of you, I instructed the attorney general to write a regulation that would rein in the proliferation of ghost guns because I was having trouble getting anything passed in the Congress," Biden said.
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The rule goes into effect 120 days from the date of publication in the Federal Register.
For years, federal officials have been sounding the alarm about an increasing black market for homemade, military-style semi-automatic rifles and handguns. As well as turning up more frequently at crime scenes, ghost guns have been increasingly encountered when federal agents buy guns in undercover operations from gang members and other criminals.
Some states, like California, have enacted laws in recent years to require serial numbers to be stamped on ghost guns.
The Associated Press and ABC News contributed to this report.