By MARK SCOLFORO, Associated Press

HARRISBURG, Pa. (AP) — Pennsylvania's top prosecutor said Monday he has told state police to treat unassembled “ghost guns” as firearms under state law, meaning felons may not legally possess them.

Democratic Attorney General Josh Shapiro issued a legal opinion to the Pennsylvania State Police that the gun frames, also known as “80% receivers," qualify as firearms.

The guns can be quickly assembled and lack serial numbers, so they cannot be traced. Purchases have not been subject to mandatory background checks.

Shapiro's opinion, in the form of a letter issued Monday to the state police commissioner, Col. Robert Evanchick, says the ghost guns are firearms if they are designed to expel a projectile by the action of an explosive, or if they can be readily converted to do so.

“No single factor is dispositive," Shapiro told Evanchick. The police “must weigh all the applicable factors together to determine whether a receiver ‘may be readily converted’ to expel any projectile by the action of an explosive.”

Shapiro said the guns are increasingly being found in the hands of people who are barred from possessing firearms. He said the attorney general's office found felons purchasing the kits at recent gun shows in the Philadelphia suburbs, York and Harrisburg. More than 100 ghost guns have been seized from prohibited purchasers in Philadelphia this year, he said.

“This presents a significant threat to public safety,” Shapiro said.

The state police plans to issue guidance about what that means for gun shops and other sellers.

Shapiro called the gun kits “new, inventive and dangerous weaponry."

Shapiro's office said several other states are considering what to do about ghost guns. New Jersey Democratic Gov. Phil Murphy signed a bill in November 2018 that bars the purchase of separate parts or kits that could be used to manufacture a firearm not traceable by law enforcement.

New Jersey lawmakers said that measure was designed to give the court system the capacity to block criminals from using technology to make weapons.