Interesting notion about "showing signs" is that I have noticed on this board when somebody is disarmed because of such concerns, people fly into a frenzy over the violation of the second amendment. Graphic writing and imagination, depression, etc., aren't necessarily signs that a person will become a mass murderer. Edgar Allen Poe and Stephen King should be (should have been) dealt with accordingly if that was the case.
The people who are most likely to do what Lanza did are not the same as those you describe and need pointed out before fears set in (with good reason). IMO he (Lanza) was not diagnosed properly and there is proof already out as well as more to come.
Two problems I see with mental illness that need attention IMHO:
1) Sloppy work by mental health doctors is increasingly risking the safety of everyone and there is no real set of checks and balances to prevent it. I have seen it on many occasions. I have tried to deal with it but the mental health organization is very powerful and don't take complaints seriously.
Likely due to many family members who are dealing with the frustrations of an ill family member. They tend to lash out at doctors and mental health organization's. In response defenses go up and real problems get buried in the muck. It often takes an act of congress(figuratively speaking) for just one problem with just one patient or dr. to be acknowledged.
One example of MHS problems written by a Psychiatrist here:
http://www.heritage.org/research/reports/2011/12/how-to-bring-sanity-to-our-mental-health-system
2) Patient rights being used as a means to defend outside influences and control patients through fear.
I have a brother that has been in and out of state mental health hospitals and housing. He has had three different diagnosis over the past 27 years. He has been on every medication for mental illness that you can imagine. He became a human guinea pig. Not able to find the real diagnosis really put him and the family through years of turbulence. When approached by the family requesting a change of doctors and facility to somewhere else we were told that my brother would have to sign his rights away and that do psychiatrist/psychologist would treat him if he did sign. We thought it a joke and decided to ask around first. Turns out that no one who took Medicaid/Medicare would take him as a patient without signing his rights to them first. Within two days my brother was contacted and threatened to lose his housing as well. He was scared and refused to sign.
We contacted two Lawyers who made it very simple for us. We did not have the money to fight it. We did not have the time (years) to fight it. Finally neither would commit to this kind of fight and recommended other avenues. The system (by design) made it hard enough (as it usually does) to make us go away.
They finally found a combination of medication to stabilize him through trial and error in 2000. A few years ago the only medication that worked was banned by the FDA and 3 years later he is more stable but nothing like he was.
Just by accident the true nature of his sudden illness was revealed when his right jaw sagged and started to look like Sylvester Stalone. His mind was the same, just unable to move or feel the right side of his face. He was taken in to have a series of test for stroke. During a CAT scan it was determined that he had a stroke, however the stroke was several years old. The eventual diagnosis for his current condition was an infection in the nerves and antibiotics cured it up. So it turns out that my brother had a stroke that was missed back in 1985 and just discovered in 2010.
Just another example very similar to what my family has went through dealing with the system here:
http://online.wsj.com/news/articles/SB10001424127887323463704578495154217291958
Here Dr. Kieth goes into some detail about Lanza and problems with the MHS:
http://www.foxnews.com/opinion/2012/12/17/why-cant-america-care-for-mentally-ill/
Not only does he point out that the guns were not the problem ( in his opinion) but the problems that plague the mentally ill and cause these problems to become more dangerous as we go on with a broken MHS.
What is wrong, exactly?
Here is the truth: Today, even a mentally ill young man with a known propensity for violence, or even a history of serious violence, is likely to receive just an hour a week of counseling (if that) by a social worker.
He is likely have an unclear diagnosis of his condition and to be on a list of constantly changing, very powerful psychoactive medications prescribed by a nurse.
He is also likely to be turned away -- repeatedly --by emergency room social workers who act as gatekeepers for insurance companies to restrict access to inpatient psychiatric treatment.
If admitted to a psychiatric hospital, he will likely be triaged quickly through an often-incompetent “tune up” of medications that might accomplish nothing and then be sent back home as soon as he “contracts for safety”—simply promising a social worker that he won’t kill anyone.
The biggest concern for me (as well as others) today with changes in the MHS is that anyone who might have some depression or emotional issues on medication will be disallowed to own or possess a firearm. Understandable and scary that it can be a power source capable exploitation whether through intention or not. However we can't ignore issues with the MHS that threaten A2 rights through their shortcomings. There can and should be changes. The question is how while leaving 2A secure. Though I don't have the answer I believe that it is possible for the right people to get together and come up with a reasonable solution before the Antis can exploit the problem and abuse it. Not only that it is better that something is done than to ignore it and allow it to be exploited. Wait too long and reversing the damage is unlikely.