Looking at these sources side by side
U.S. Executions Since 1976
http://www.disastercenter.com/crime/uscrime.htm
I see an interesting picture emerge.
From 1966 to 1980, the murder rate nation wide very nearly doubled (from 5.6 to 10.2 per 100,000)
In this time, a grand total of four people were put to death.
1 in 1966
1 in 1977
2 in 1979
1980 was the peak of the nationwide murder rate. Nobody was executed in 1980.
And then, executions slowly increased from year to year... the murder rate kind of went back and forth, never again getting as high as it was in 1980.. then it fell in 1994 and kept on dropping till about 2001. At that point, the murder rate kept at a steady average of 5.5 per 100,000 (never above 5.7, never below 5.4)
1999 saw the most number of executions in any year... 98.
2000 saw a decrease in murder rate from 5.7 to 5.5 per 100,000... even with an increase in population by more than 8 million.
From 2001 till 2008, the average number of executions per year was 56.
Never more than 71, never less than 35.
Those years saw very nearly half the murder rate as 77-82, when executions per year were still in low single digits.