If the death penalty is murder...
Then arrests are kidnapping...
Taxation and fines are theft...
Zoning is squatting...
Eminent domain is extortion...
We do need to scale back on the way that the death penalty is applied in the United States, including by providing far more protections to those who are accused of a capital crime. However, as shown above, to call execution a form of murder logically opens the door to a whole score of other arguments, none of which even the most ardent opponent of the death penalty would ever take seriously.

Yes, besides ignoring the plain meaning of the word "murder," which is a legal term rather than a moral one.
Unless one is applying it to crows, in which case it's a funny name from a flock.
We do not need to scale back in the USA. We need to expedite. When a killer can be suppoorted and get a free education, medical and room and board 15 years after he has been sentenced to death.... that is a state crime.
If one innocent person is executed to expedite the execution of 99, then so be it. In most cases, the person has committed many crimes and it is only this murder there is doubt about.
When execution is truly used, crime will drop.
Well I sure would hate to be that 1!! Is that somehow an acceptable percentage of lives and families destroyed? Has not the fact that prosecutors regularly trump up and even fabricate charges against individuals been proven to your satisfaction?
Until prosecutors/DAs can and ARE prosecuted for false charges I won't trust our so-called justice system.
There's just one little problem with your idea. Too many people are being found innocent because prosecutors frequently don't give a rodent's posterior about getting the right guy so long as they have a warm body to toss in prison and a notch on their belt. Do a little digging on the previous Dallas DA if you need an example.
For your benefit. This is a perfect example of how the police and prosecutors often take a devil-may-care attitude these days.