Did Pope Francis declare that according to the teaching of the Catholic Church capital punishment is intrisically evil?
The straight answer is NO.
Did Pope Francis indeed declare the capital punishment to be intrisincally evil, that is, sinful under any and all circumstances, even if / when effective incarcerination is impossible?
The answer is NO again.
Or did he (merely?) state that since in contemporary times effective incarcerination is possible, it should always be used instead of capital punishment?
The answer is again NO.
This statement can be more inter-related to St.John Paul II during the development or changes in CCC2267 from 1992 to 1997.
Below is the excerpt of the reasons behind St.John Paul II changing the CCC2267 in 1997.
...under Pope John Paul II in 1992, says on the matter: “Assuming that the guilty party’s identity and responsibility have been fully determined, the traditional teaching of the Church does not exclude recourse to the death penalty, if this is the only possible way of effectively defending human lives against the unjust aggressor.”
The former formula does stipulate that if non-lethal means are sufficient to protect people’s safety from the aggressor, then authority must limit itself to it, as these “are more in keeping with the concrete conditions of the common good and more in conformity to the dignity of the human person.”
In 1997, the Catechism was changed to reflect John Paul’s 1995 encyclical Evangelium Vitae.
The addition said that the cases in which the execution of the offender is an absolute necessity “are very rare, if not practically nonexistent.”
Pope Francis changes teaching on death penalty, it’s ‘inadmissible’
With regards to Pope Francis reasons for adding additional changes to CCC2267 as the Prefect of the Congregation for the Doctrine of the Faith, Spanish Cardinal Luis Ladaria.
According to Ladaria, the new formulation of the Catechism expresses “an authentic development of doctrine that is not in contradiction with the prior teachings of the Magisterium.”
As it’s been re-written, the Catechism now also says that “Recourse to the death penalty on the part of legitimate authority, following a fair trial, was long considered an appropriate response to the gravity of certain crimes and an acceptable, albeit extreme, means of safeguarding the common good.”
Yet today, “there is an increasing awareness that the dignity of the person is not lost even after the commission of very serious crimes. In addition, a new understanding has emerged of the significance of penal sanctions imposed by the state.”
“Lastly, more effective systems of detention have been developed, which ensure the due protection of citizens but, at the same time, do not definitively deprive the guilty of the possibility of redemption,” reads the Catechism now, as it was approved by Francis.
It’s for this reason, and “in light of the Gospel,” that the Church teaches that the practice is now inadmissible.
In it, he explains the decision, saying it was Francis who on the occasion of the 25th anniversary of the promulgation of the Catechism, had asked for the teaching on the death penalty to be reformulated to “better reflect the development of the doctrine on this point.”
Below are the statement of Pope Francis;
1.The Vatican said Thursday Aug. 2, 2018 that Pope Francis had changed the Catechism of the Catholic Church about the death penalty, saying it can never be sanctioned because it "attacks" the inherent dignity of all humans.
2.“The death penalty is inadmissible because it is an attack on the inviolability and dignity of the person,”
3.The pope’s words came on Oct. 11, when Pope Francis said that capital punishment “heavily wounds human dignity” and is an “inhuman measure.”
4.“It is, in itself, contrary to the Gospel, because a decision is voluntarily made to suppress a human life, which is always sacred in the eyes of the Creator and of whom, in the last analysis, only God can be the true judge and guarantor,” he said.
The statement released by the Vatican’s press office says that Pope Francis approved the new changes to point number 2267 of the Catechism on May 11, 2018
Pope Francis changes teaching on death penalty, it’s ‘inadmissible’
Your other statement of inquiry can be answer directly by Catechism of the Catholic Church like;
The distinction seems to matter because the question whether in contemporary times the States can, in all, even most extreme cases, effectively protect the lives of their citizens without capital punishment seems to not belong to the scope of "morals and faith", which is the scope of the teaching of the Church.
Duties of civil authorities
2235 Those who exercise authority should do so as a service. "Whoever would be great among you must be your servant."41 The exercise of authority is measured morally in terms of its divine origin, its reasonable nature and its specific object. No one can command or establish what is contrary to the dignity of persons and the natural law.
2236 The exercise of authority is meant to give outward expression to a just hierarchy of values in order to facilitate the exercise of freedom and responsibility by all. Those in authority should practice distributive justice wisely, taking account of the needs and contribution of each, with a view to harmony and peace. They should take care that the regulations and measures they adopt are not a source of temptation by setting personal interest against that of the community.42
2237 Political authorities are obliged to respect the fundamental rights of the human person. They will dispense justice humanely by respecting the rights of everyone, especially of families and the disadvantaged.
The political rights attached to citizenship can and should be granted according to the requirements of the common good. They cannot be suspended by public authorities without legitimate and proportionate reasons. Political rights are meant to be exercised for the common good of the nation and the human community.
Lastly, your asking if your interpretation is correct citing your conclusion below:
However, I have feeling, in many cases, including this one, Pope Francis amends this part of the teaching of the Church, saying that physical violence may only be permissible as a response to immediate threat, but never to a recurring threat. Which is why it may still be permissible for a police officer to shoot down a Mafia hitman if in any other case this Mafia hitman would shoot down the police officer instead; but it is not permissible to sentence said hitman to capital punishment even if because of the ongoing war with Mafia rebels he cannot be effectively imprisoned for a prolonged time. Is this interpretation correct?
You personal interpretation is incorrect as the basis for the changes in CCC2267 does not reflect your examples.
The strong words and basis of Pope Francis is this;
With the papacy of Pope Francis, the issue came to the forefront again. He publicly expressed his support for the abolition of the death penalty in 2013 and 2014, and in 2015 used even stronger language:
Today capital punishment is unacceptable, however serious the condemned’s crime may have been. [...] The death penalty is contrary to the meaning of humanitas and to divine mercy, which must be models for human justice. (letter to the International Commission against the Death Penalty)
Taken from Nathaniel's answer on a related question: What is the Catholic Church's historical position on capital punishment: how did we get here?.
In closing, Pope Francis core message is the heart of the Gospel which is the the Divine Mercy echoing the words of Pope Emeritus Benedict XVI. The Mission of Christ in the gospel is to redeem all of us including all the sinners and He paid a high price for this. Jesus offered His very own life for all of us to restore sanctity and dignity of the life He had given us. Jesus is the Author of Life and we are commanded that no one can take the life of anyone.
And there is no soul no matter how grave & heinous crime he committed that cannot be redeemed by the Most Precious Blood of Christ, but only if the sinner's like the Prodigal Son come to his senses and acknowledge his sins and mistakes and come forward to the loving & merciful embraced Abba Father.
The language of Divine Mercy transcends orthodoxy it can only be fathom by men who reach the supernatural state.
This has been the advocacy of the two predecessor's of Pope Francis namely St.John Paul II the Great and Pope Emeritus Benedict XVI.
It's no wonder why the Holy Spirit inspires Pope Francis to clear the gray area in the death penalty attributing it to the Infinite Mercy of God.
As Pope Francis clearly said;
"The Divine Mercy is Infinite but the Time of Mercy is Not".