Handing over a murderer to the Goel Hadam?

Question

וְשָׁלְחוּ זִקְנֵי עִירוֹ וְלָקְחוּ אֹתוֹ מִשָּׁם וְנָתְנוּ אֹתוֹ בְּיַד גֹּאֵל הַדָּם וָמֵת.

The elders of his city must take him [the intentional murderer] and hand him over to the blood avenger, and he shall die.

-Devarim 19:12

This is in the parsha of the unintentional murderer, where after specifying that a person guilty of culpable homicide is allowed to live in a city of refuge (or a Levite city), the Torah then deals with someone who intentionally killed another. Here the verse states that he is handed over to the blood avenger.

Is this literally so? My understanding is that if there are witnesses and a warning (עדים והתראה), then a murderer is sentenced to death, and the witnesses themselves are to be the executioners. Where exactly in halacha is a "blood avenger" given the right to execute a killer? Or is this one of the places where the Oral Torah overrides the simple understanding of the Written Torah?

Answer 1

The law is exactly in accordance with the literal meaning of the verse in this case. "ונתנו אותו ביד גואל הדם"

The Rambam codified this ruling in the halacha immediately following the halacha cited in @Danny Schoemann's now deleted response:

רמב"ם הלכות רוצח ושמירת הנפש א:ב
‏ מִצְוָה בְּיַד גּוֹאֵל הַדָּם [לַהֲרֹג אֶת הָרוֹצֵחַ] שֶׁנֶּאֱמַר (במדבר לה-יט) 'גֹּאֵל הַדָּם הוּא יָמִית אֶת הָרֹצֵחַ'.‏

From the previous halacha in the Rambam and from the pasuk it is clear that this is the court giving the job of executioner to the גואל הדם.

Answer 2

There is actually a contradiction in the Rambam who should kill him, the Goel Hadam or the witnesses.

As @Daniel posted, the Rambam in Hilchos Rotzeach Ushmiras Nefesh 1:2 writes:

מצוה ביד גואל הדם [להרג את הרוצח] שנאמר (במדבר לה יט) "גאל הדם הוא ימית את הרצח".

There is a Mitzva for the Goel Hadam to be the one to kill the Murderer as the Passuk states "The Goel Hadam should put the murderer to death."

While the Rambam in Hilchos Sanhedrin 13:1 writes as @Shaul_Behr suggested:

ורוצח שלא הרגוהו עדיו חיבין להמיתו ביד כל אדם.

If the witnesses do not kill him (the murderer), then anyone else kills him.

The Aruch Hashulchan answers the contradiction in Choshen Mishpat 425:2 by saying that the Rambam understands that the primary Mitzva is for the Goel Hadam to kill the Rotzeach. If he doesn't, then the Eidim should kill him, and if they don't, then anyone else should:

וצ"ל דס"ל להרמב"ם ז"ל דעיקר המצוה היא ביד גואל הדם ואם לאו ב"ד מצוין להעדים שימיתוהו ואם לאו מיתתו ביד כל אדם וצריך לדחוק סוגית הש"ס בסנה' לפירושו ע"ש:

There are a number of other ways to answer the contradiction. You can find Maareh Mekomos in the Mafteach in the back of the Frenkel Rambam on Hilchos Rotzeach Ushmiras Nefesh 1:2.

Parenthetically, the Rambam in Pirush Mishnayos to Sanhedrim 7:3 gives a good reason why it should be the Eidim who kill a person who is Chayav Missah (in general, not specifically by a murderer), because they're the ones who actually saw it firsthand: וכבר ידעת שהעדים הם שממיתין בידים איזו מיתה שתהיה לפי שאותו הדבר אצלם אמת שהשיגוהו בחושיהם והוא אצלנו ספור דברים שאין אנו יודעים אלא מה ששמענו מהם ולפיכך צוה השם יתברך שיהיו העדים ממונין על הענין וזהו ענין נאה.