Murder is the illegal killing of a person
If its state sponsored its not illegal. If its not illegal it's not murder.
It should be, and it is if it is a juvenile according to international law.
The US Death Penalty and International Law: US Compliance with the Torture and Race Conventions | Death Penalty Information Center
Juveniles
Although the death penalty is generally tolerated under international law, the same cannot be said of the execution of juvenile offenders. The International Covenant on Civil and Political Rights requires that the death penalty only be imposed "for the most serious crimes," and never upon those who were under 18 years of age at the time of their crime.5 Virtually all the countries of the world have signed or ratified this important treaty, including most recently, China. However, the United States is the only country with an outstanding reservation to the Article forbidding the execution of juvenile offenders.
Only seven other countries in the world are known to have carried out an execution of a juvenile in the last ten years6 and the U.S. may be the most flagrant violator with 3 more juvenile offenders executed just this year. Since 1976, there have been 12 executions of those who were under 18 at the time of their crime in the U.S., with 9 of the 12 occurring in the 1990s. Seventy-two additional juveniles are on death row awaiting execution. While some states and the federal law set 18 as the minimum age of eligibility for the death penalty, the majority of death penalty states allow 16 or 17 year-olds to receive this ultimate punishment.7And some government officials have been calling for a reduction of the minimum age, even to as low as 11.8
It is because of this history and practice that the U.S. took a specific reservation to the Civil and Political Rights Covenant essentially exempting itself from the ban on juvenile executions. The U.S. has also taken a reservation to the Torture Convention, stating that we understand "international law does not prohibit the death penalty, and does not consider this convention to restrict or prohibit the United States from applying the death penalty consistent with the Fifth, Eighth and/or Fourteenth Amendments to the Constitution . . . ." In other words, what the U.S. considers to be lawful punishment under the Torture Convention is what the U.S. courts, not the world community, consider lawful.
Reservations to treaties, including human rights agreements, are generally recognized in international law. However, reservations which contradict the "object and purpose" of the treaty are not allowed. Eleven countries formally protested the U.S.'s reservation to the Civil and Political Rights Convention regarding juvenile offenders, and the U.N. Committee on Human Rights has stated that such a reservation is invalid. The U.S. Senate responded to this challenge by threatening to withhold funds from U.S. participation in the work of the U.N. Committee on Human Rights.9