The biggest problem is that mental health treatment is simply not available to a large proportion of society. Unless you have wealthy family in the States (or that can afford mental health insurance) it is almost impossible to get good in depth and long term treatment. Especially if you aren't an imminent danger which you essentially have to be holding the gun or standing on the railing of the bridge before they hold you. Most dangerous people aren't stupid, they won't admit to wanting to kill people until they are long past the time they needed to start getting treatment.
For the ones who do ask for help though there simply isn't the support. If you are schizophrenic for example, you often don't have a lifestyle that allows you to pay for treatment and stay in it (i won't even mention the difficulty of staying on meds if not an inpatient)
Mental health should be covered from the get go by the community, states and federal government. If we made it a norm then the stigma would go away too. I would like to see standard evaluations of teens at 15 and 18 to see if any issues are surfacing they need help dealing with as these are ages that it often comes out in.
I also agree the guns have to be stopped. I wish gun control wasn't such a hot button issue, in Canada we have strict gun control but everyone who hunts or farmers have a shotgun, so it isn't as if we stop ownership. There isn't even a registry for those (there used to be but it has been ended) Except for pistols and autojmatic weapons. We have Toronto or Vancouver that are the size of Chicago and only a handful of homicides compared to the hundreds there.