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5 things to know about 'ghost guns'

A "ghost gun" is an untraceable type of firearm that's legal and increasingly easy to obtain.

PHOENIX — Phoenix police said Tuesday that the gun used in a shooting at Cesar Chavez High School was a "ghost gun," an untraceable type of firearm that's legal and increasingly easy to obtain. 

Here are five things to know about ghost guns.

RELATED: Phoenix PD identifies, arrests 15-year-old student as Cesar Chavez High School shooting suspect

They're in pieces

A ghost gun is a term for a weapon that's made or assembled outside of a factory, usually in a person's home. They come in pieces and can be put together later. Because they're not pre-assembled, the federal government doesn't consider them a gun. 

Because of this, there is no requirement for a background check to buy the pieces. 

They're easy to buy

The parts, plans and tools are readily available online. 

Companies sell the pieces used to assemble ghost guns to almost every state. Washington is among a handful of states where ghost guns are illegal. Arizona is not one of them.

The Los Angeles City Council voted to ban them the day after the Cesar Chavez High shooting. 

There are also plans to 3D print the pieces for sale as well. 

They have to be finished at home

Ghost gun building revolves around one basic part that turns the pieces into a functional firearm. The receiver, or "lower" are legal to sell, as long as they are only 80% finished. 

That means they have to be completed by the buyer, by a process of milling out a chunk of metal or plastic, depending on the model of gun. Then, the working gun can be assembled. 

It's also possible to build the entire gun from scratch with a 3D printer.

They have no serial numbers

Because they're considered parts and not guns upon shipping, they don't have to have serial numbers. That's why they're considered untraceable.  

However, it's important to note that there is no federal, searchable or digital database of guns. Federal law prohibits the Bureau of Alcohol, Tobacco, Firearms and Explosives from creating one, so all their records are on paper and have to be hand searched. 

There's no way to know how many there are

It may seem obvious, but because there are no serial numbers, there's no way to know how many ghost guns have been manufactured. 

And that means police have no way of knowing what they're up against, said ASU School of Criminology professor Dr. Charles Katz. 

"Going in blindly is too big of an issue," Katz said. "There's really not a lot that we can say that we know definitively about their use within the general population or the criminal population."

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