I understand that ”Thou shall not murder” is a better translation.
With all due respect to the Pope, he is not making the connection that if G-d had meant for us not to kill, then there would have been no way for the ancient Israelites to comply with the Levitical laws prohibiting sex outside traditional marriage for example, laws which required offenders who broke them to be put to death.
Didn’t God order the Israelites to completely wipe out certain people groups, down to the last man, woman and child and animal? I think Israel failed to do this, on several occasions, and it always led to problems.