Guns do not load, aim and fire themselves. The typical hunter or other gun carrier does not commit mass murder.
This would be a better avenue to explore for the source of the problem, especially in Colorado:
Street drugs and schizophrenia
Overview: Use of street drugs (including LSD,methamphetamine,marijuana/hash/cannabis) and alcohol have been linked with significantly increased probability of developing psychosis and schizophrenia.
This link has been documented in over 30 different scientific studies (studies done mostly in the UK, Australia and Sweden) over the past 20 years. In one example, a study interviewed 50,000 members of the Swedish Army about their drug consumption and followed up with them later in life.
Those who were heavy consumers of cannabis at age 18 were over 600% more likely to be diagnosed with schizophrenia over the next 15 years than those did not take it. (see diagram below). Experts estimate that between 8% and 13% of all schizophrenia cases are linked to marijuna / cannabis use during teen years.
Marijuana, Cannabis and Schizophrenia - Schizophrenia.com