Several posters have talked about the possible links between mental illness and violence. I found an interesting article that really clarified the issue for me. Dr. Richard Friedman wrote a really thought-provoking piece in the New England Journal of Medicine:
Until recently, most studies have focused on the rates of violence among inpatients with mental illness or, conversely, the rates of mental illness among people who have been arrested, convicted, or incarcerated for violent crimes.1 For example, one national survey showed that the lifetime risk of schizophrenia was 5% among people convicted of homicide a prevalence that is much higher than any published rate of schizophrenia in the general population suggesting an association between schizophrenia and homicide conviction.2 These studies, however, tend to be limited by selection bias: subjects who are arrested, incarcerated, or hospitalized are by definition more likely to be violent or very ill and thus are not representative of psychiatric patients in the general population.
A more accurate and less biased assessment of the risk of violence perpetrated by the mentally ill comes from epidemiologic studies of community samples. The best known is the NIMH's Epidemiologic Catchment Area (ECA) study, which examined the rates of various psychiatric disorders in a representative sample of 17,803 subjects in five U.S. communities. Although this study was not initially designed to assess the prevalence of violent behavior, data on violence were collected for about 7000 of the subjects.3 . . .
The study showed that patients with serious mental illness those with schizophrenia, major depression, or bipolar disorder were two to three times as likely as people without such an illness to be assaultive. In absolute terms, the lifetime prevalence of violence among people with serious mental illness was 16%, as compared with 7% among people without mental illness.
http://www.nejm.org/doi/full/10.1056/NEJMp068229
While we know nothing about who killed Celina at this point, I find it interesting that all the literature Ive been reading seems to state that substance abuse is a much bigger predictor of violence than mental illness.