Commentary for Shevuot 4:2
וְחַיָּבִין עַל זְדוֹן הַשְּׁבוּעָה, וְעַל שִׁגְגָתָהּ עִם זְדוֹן הָעֵדוּת, וְאֵינָן חַיָּבִין עַל שִׁגְגָתָהּ. וּמַה הֵן חַיָּבִין עַל זְדוֹן הַשְּׁבוּעָה, קָרְבָּן עוֹלֶה וְיוֹרֵד:
And they are liable [for an oleh veyored offering] for willfulness in the oath, ["and it be hidden" not being written in this connection], and for unwittingness with willfulness in (withholding) testimony, [i.e., where they know that the oath is forbidden, but not that it makes them liable for an offering.] And they are not liable for unwittingness [if they were completely unwitting, assuming that they had no testimony for him, and then remembered. For in that instance they could not help it, and (Leviticus 5:22): "…and he swear falsely, etc." does not apply to them.] And for what are they liable for willfulness in the oath? For an oleh veyored offering.
Bartenura on Mishnah Shevuot
English Explanation of Mishnah Shevuot
And what are they liable for the intentional transgression of the oath? A sliding scale sacrifice.
This mishnah continues the lists we have seen in the previous three mishnayoth.
There are two elements to the false oath of testimony: 1) knowing information and intentionally withholding it; 2) intentionally swearing falsely that one does not know the information. The mishnah teaches that if the witnesses intentionally deny knowledge of the testimony, even if they don’t realize that swearing falsely is forbidden, they are liable for intentionally swearing falsely. However, if they don’t realize that they know information then they are not liable, since this was a totally unintentional transgression. In other words, there punishment hinges upon their intentional denial of knowledge of information. If they intentionally withheld information and swore to it, then they are liable to bring a sliding scale sacrifice, as described in Leviticus 5:5-13.