It seems that people with depression are more likely to commit murder.
In this study, Homicide is strongly correlated to depression and not to mania, the authors concluded:
Typical manic episodes could be the cause of penal infractions, usually benign. In contrast, forensic studies show a close relationship between depression, suicide and homicide. Killers (16-28%) are often depressed when they commit a crime. In the UK and USA, 4-35% of killers commit suicide immediately after their crime.
In another study, The role of depression in couples involved in murder-suicide and homicide.
, the authors concluded:
Twelve couples in cases of murder-suicide were compared to 24 couples in cases of homicide during the period 1978 to 1987 in Albuquerque, N.M. Data were obtained from police, the courts, hospital records, and interviews with friends and family of the deceased. The most striking findings were that perpetrators of murder-suicide were depressed (75%) and men (95%), while perpetrators of homicide were not depressed and one-half were women. The data indicate that the murder-suicide and homicide groups are two different populations.
As for recent studies, a new study suggested that people with depression might be more likely to commit a violent crime than those without depression.
Researchers analyzed data from more than 47,000 people in Sweden who were diagnosed with depression and followed for an average of three years. They were compared to more than 898,000 gender- and age-matched people without depression.
People with depression were five to six times more likely than those in the general population to harm others or themselves, according to the researchers at Oxford University in England.