How much salt it would take to kill a person will depend on various factors such as age and weight. For a 220 pound man that would be 300 grams which is just shy of 10 ounces. the lowest published lethal dose for humans is a third of that.
1 Additional Answer
Salt in very large quantities can kill a person or the weight of about one hundred pounds of salt can kill you too. Salt has been used in developing countries to kill newborn babies as well. Evidence of death by salt would be detected right away.