You're talking the difference between punishment under the penal system for crimes committed - a bit different than trying to stop a large-scale murder that is in the mill.
One case is someone stole your daughter's car and has been through the process.
The other scenario is the person has kidnapped your daughter and she will die a horrible death if you don't get info from him right now - what constraints do you put on yourself?
By calling it murder you've opened the door to treating it as a crime, under the penal system, and not as war-like acts. — Moreover, the 8th is not constrained to the penal system, or do you assert that the $X-thousand/day fines the EPA imposes on individuals are not covered under the 8th?
One case is someone stole your daughter's car and has been through the process.
The other scenario is the person has kidnapped your daughter and she will die a horrible death if you don't get info from him right now - what constraints do you put on yourself?
Rather contrived, but it also shows an apparent & interesting assumption on your part: that the Constitution is for restraining individuals and not government.