Note that rigor mortis has maintained the position of his arms after the shotgun has been removed. Rigor mortis occurs because metabolic activity continues in the muscle after death. So long as the store of glycogen in a muscle is sufficient to permit the regeneration of ATP by the formation of lactic acid, the muscle remains lax. When its store of glycogen is exhausted, the concentration of ATP falls, and the muscle becomes rigid because of the formation of abnormal links between actin and myosin. The rigor mortis persists until these links are destroyed by advancing autolysis.
Suicide is a risk for people with depression.
Also, substance use, especially alcohol, is highly correlated with homicide and suicide. Note the beer cans in the background.