Kasie would be able to match the caliber from bullets used in the shooting. But rifling is unique to each firearm. Only a firearms used in a crime would be in a database. Kasie would need the firearm itself to match rifling patterns. Registration is voluntary.
'Ghost guns' can exist. Although a person can build a gun in this manner, the receiver requires a background check to purchase and it certainly has a serial number - unless it is finished to less than 80% complete. All the other parts will not fire a bullet without the receiver and would just be toys. And, all of this depends on individual state laws.
Near the end the recently released prisoner is about to meet his daughter. When he gets out of the car he has a large bottle of jam in his hand. When he hugs his daughter his hands are empty. However, there's a shot where he puts the bottle in his jacket pocket as he's getting out of the car.
Torres and Bishop get off the lift wearing covid masks then immediately remove them. In the international desks all the other staff are wearing their masks. At the time all staff should have been wearing masks in the office not pick and choose government rules.
McGee recommends a chiropractor to Palmer. He is, throughout the whole show, a rational, scientifically minded sceptic and would be unlikely to espouse chiropractic. Later on, Palmer is praising the benefits of the chiropractor's treatment. As a medical and scientific professional, he is even less likely than McGee to place any faith in chiropractic.
Timeline is totally all over the place in this episode. Covid masks, posters and restrictions are all over the place and Palmer says his wife died from covid a while ago. If she did in deed die from covid it should have been mentioned in previous episodes, so obviously first 6 episodes were filmed and meant to be broadcast in previous season and episode 7 is first of new season. The whole timeline is all over the place.