What this demonstrates is that a crazy person who wants to kill people will find a way to do so. Illegal firearms, like any illegal substance, can be obtained if someone wants them badly enough. The only way to stop mass shootings is to have more first responders on scene to neutralize the threat. That means more police or properly trained civilians with private firearms. As even in a police state you can't have an officer everywhere, the most reasonable response is properly trained civilians licensed to carry a firearm.
I would much prefer that humanity gave up its violent tendencies en masse, and we lost all need for firearms. We're not there yet. As a result, our approach to the issue must be pragmatic, not idealistic. Until we change our basic tendency toward violence, it does not matter which tools of violence we ban or restrict.
Finnish Firearms Laws (note, this is from Wikipedia, but naturally you may research Finnish firearms laws if you're interested):
The ownership and use of firearms is regulated by the Firearms Act of 1998.
Firearms can only be obtained with an acquisition license, which can be applied for at the local police for €32. A separate license is required for each individual firearm and family members can have parallel licenses to use the same firearm. According to law, the firearms must be stored in a locked space or otherwise locked, or with vital parts removed and separated. Even then the weapon or any of its separated parts must not be easily stolen. If an especially dangerous firearm or more than 5 pistols, revolvers or self-loading rifles or other-type firearms are being stored, they must be stored in a certified gun safe or in a secure space inspected and approved by the local police authority.
They may be carried only when they are transported from their place of storage to the place of use (shooting range, hunting area or such). Even then they must be unloaded and concealed or kept in carrying pouches. Aside from law enforcement agents and military personnel, only security guards with closely defined working conditions, special training and a permit are allowed to carry a loaded gun in public places. The ownership of air-rifles is not regulated but carrying or firing them in public places is not permitted. A crossbow is paralleled to an air rifle in legal matters.
To obtain a firearms license, an individual must declare a valid reason to own a gun. Acceptable reasons include hunting, sports or hobby shooting, profession related, show or promotion or exhibition, collection or museum, souvenir, and signalling. It is worth noticing that self- or home defence are not considered valid reasons. The applicant must provide evidence supporting the acquisition license application to prove that he or she is actually using firearms for the stated purpose(s). Such proof may consist of written declarations from other license holders as referees, shooting diaries or certificates from a shooting club.
The applicant is also subjected to an extensive background check from police accessible databases and even citations for speeding or DUI can be grounds of not granting the license.