Investigators believe the deaths came from either a "murder-suicide" or a "double suicide, " he said.

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The incident came five weeks after a double suicide-bombing, also in Jerusalem, had killed 14 shoppers and workers at a market.

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Last week a double suicide attack at a munitions plant in the town of Wah in Punjab province left nearly 70 people dead.

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And there is always the risk of a double love-suicide.

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They found that children raised by one parent had more than double the risk of suicide attempt and alcohol-related disease.

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The man turned out to be a double agent who exploded a suicide vest, killing five CIA operatives and two contractors in late 2009.

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Armed CIA drones frequently buzzed overhead, searching for targets as some of the world's most sought-after terrorists trained suicide bombers, cultivated double agents and orchestrated political assassinations.

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The double effect means that to get the suicide process working efficiently, it would have to be restarted at two separate points.

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