Police originally believed that Trevor Buchanan and Lesley Howell had died in a suicidepact after discovering that their partners were having an affair.
In March 2010, Francisco Lotero and Mariam Coletti shot two of their children before killing themselves after making a suicidepact over fears about effects of global warming.
Weeks after the drink incident, Howell gassed his wife and Mrs Stewart's policeman husband Mr Buchanan, before making it look like they had died in a suicidepact.
The two sides agreed to a suicidepact if they couldn't reach agreement - tax rises and defence spending cuts the Republicans loathe - as well as other spending cuts that are offensive to Democrats.