In any country that leaves the ability to purchase weapons by the public- the purchaser is still the one who is responsible for how it is used. In some cases, you have to meet certain requirements like taking a safety class, have a license, pass a back ground check in the criminal records department- and many more actions/qualifications to obtain a weapon.
There is no real win-win situation with gun control unless the gun user is a respectable, law abiding citizen who is mentally stable, mature, knowledgeable of how to properly store and fire the weapon, cares enough about the lives of others, will not use it improperly, obtains the needed and legal requirements to own one in the first place, obtains the gun legally, and above all- does not blame the gun's existence for being the root of the reason for it being evil.
Any item can become a weapon. It becomes a weapon when something intelligent uses it in a manner to purposefully do harm or bring death and destruction to others.
This is a sad act of unwanted death and harm. Unfortunately, this person chose to do this act and it was a planned- there was no stopping this from happening and obviously he obtained what he wanted in order to carry out this disgusting act, regardless all of the attempts at keeping weapons out of the hands of people who choose to do such a malicious crime.
My sympathy to the families and the victims, and may they find comfort in answered prayers.