Caret for an intentional Sin punishable by Death when there are no witnesses

Question

We know that Sins punishable by death are punished when there are witnesses and warning. We also know that when there are no witnesses, but the sin is made intentionally, the punishment is Caret (1). What is the source in Gemara for this last rule? I found in several Gemarot that there is Qorban Chatat only for sins that are punishable by Caret when intentionally made.

״וְכִי תִשְׁגּוּ וְלֹא תַעֲשׂוּ אֵת כׇּל הַמִּצְוֹת הָאֵלֶּה״, וּכְתִיב: ״וְהַנֶּפֶשׁ אֲשֶׁר תַּעֲשֶׂה בְּיָד רָמָה״. הוּקְשׁוּ כּוּלָּם לַעֲבוֹדָה זָרָה: מָה לְהַלָּן דָּבָר שֶׁחַיָּיבִים עַל זְדוֹנוֹ כָּרֵת וְשִׁגְגָתוֹ חַטָּאת, אַף כׇּל דָּבָר שֶׁחַיָּיבִין עַל זְדוֹנוֹ כָּרֵת וְעַל שִׁגְגָתוֹ חַטָּאת.‏

But I don't find the rule that a sin punishable by death penalty is punishable by Caret when there is no witnesses.

I know that the Gemara in the third chapter of Ketubot says that Chyuve Mita, the sentence is executed by events when there is no Bet Din. But this is an other issue.

I know that in Bamidbar 15, Megadef is Caret. But for Rabanan (Keretot 7b and Pesachim 93b) it's to sing for Avoda Zara, not punished by death penalty, and for Rabbi I assume that is to curse Hashem without the name of Hashem, following Sanhedrin 56a.

(1): See Sefer Hamitzvot from the Rambam Lo Taase 352.

וכן התבאר לך שכל מי שנתחייב מיתה בבית דין איזו מיתה שתהיה הנה האיש ההוא בכרת גם כן כשלא המיתוהו בית דין או לא נודע לו, מלבד עשרה אנשים שהם מחוייבי מיתת בית דין ואין עליהן כרת והם מסית ומדיח ונביא שקר ומתנבא בשם ע''ז וזקן ממרא ובן סורר ומורה וגונב נפש מישראל ורוצח ומכה אביו ואמו ומקלל אביו ואמו, וכל אחד מאלו כשנחקרה עליו העדות יהרג, ואם לא יהרג שלא יוכלו בית דין להרגו או לא נודע לו הנה הוא מתיר עצמו למיתה אבל אינו עומד בכרת. ושמור אלו השרשים וזכור אותם

Translation (From Sefaria).

And likewise has it been made clear to you that anyone who is liable for a death penalty of the court - whatever death penalty it may be - behold, that man is also [punished] with excision, when the court did not kill him or it it did not know about it - except for ten cases... etc... And hold on to these principles and remember them.

Megadef is not included in the list of exceptions.

Answer 1

As I mentioned in the comments to the question, I don't believe such a rule exists. That is, the following types of sin all exist:

1. A sin which incurs the death penalty when done intentionally in the presence of witnesses, and karet when done intentionally without witnesses.

2. A sin which incurs the death penalty when done intentionally in the presence of witnesses, but never karet.

3. A sin which never incurs the death penalty, but does incur karet when done intentionally. (See Rambam Hilchot Sanhedrin 19:1 for a list of these 21 sins.)

4. A sin which incurs neither the death penalty, nor karet.

Rambam gives a list of 36 cases for which there is a death penalty Hilchot Sanhedrin 15:10-13, and a list of 48 (=43+2+3) sins for which there is karet (Hilchot Shegagot 1:2-4). By comparing these lists, one finds the following cases which do incur a death penalty but never incur karet:

• a person who entices others to worship idols (מסית)
• the people who lead a city to idol worship (מדיח)
• a sorcerer (מכשף)
• a person who curses his father or his mother (מקלל אביו או אמו)
• a wayward and rebellious son (בן סורר ומורה)
• a murderer (רוצח)
• a person who wounds his father or mother (חובל באביו או באמו)
• a person who kidnaps a fellow Jew (גונב נפש בישראל)
• a rebellious elder (זקן ממרא)
• a false prophet (נביא שקר)
• a person who prophesies in the name of a false deity (מתנבא בשם ע"ז).