Um...no. They are both simply true statements. How does the second argument negate the first? They have nothing to do with each other. A man walked into an unarmed school and killed people with a weapon, one that was specifically banned from the premises. Gun murder in a gun free zone. Effectively guns were banned on the premises, yet it still happened. So yes, when guns are banned, a determined murderer will still find a way to kill people.
Your argument is based on the premise that if guns are banned, they will just magically disappear. The guy could have just as easily made a bomb vest and murdered everyone that way, or pulled an Oklahoma city. So your argument, such as it is, is ridiculous.