The Constitution explicitly forbids ex-post facto laws. Any attempt to execute someone for a crime commited in the 1960’s using a law passed in 1972 would seem to me to run afoul of the Constitution. You have to be tried under the laws in effect at the time of the crime.
I stand corrected on one point. One of the killers did commit his 1st Murder 1 in 1966 and got life. He was mercifully freed and did an encore performance in ‘78. He has been on Death Row since ‘81 for that one.
On the other point, I stand by my statement. There are numerous guys on Death Row since mid-70’s, one guy since ‘74. Several of these guys could be on Social Security.