What is the meaning of "Yachpesu Olos"?
Rashi: They seek Alilos (pretexts) - "Havu va'Ayin Ilah Lehashkachah l'Daniel" (Daniel 6:5).
Radak: "Olos" is like Avlos (sins). These slanderers and evil tellers are people of deception and fraud. They seek and investigate in their hearts sins and schemes.
Malbim: They search to show that David sinned in order to justify their deeds, that he is Chayav Misah.
What is the meaning of "Tamnu"?
Rashi: They hid 1 [their hearts and did not reveal their intent].
Radak: This is like Tamemu. The Nun is in place of the latter Mem. It means totally. (Refer to 64:7:3:3.)
Minchas Shai: An old printing, a Sefardi Kesav Yad and Rashi's text have a Tes in Tamnu. Our texts, Mesores ha'Gadol, Ibn Ezra, Radak [and other Meforshim] have a Tov.
What is "v'Kerev Ish"?
Rashi: Each man of them hides his thoughts.
Radak: As much as you can search and investigate his heart and inner thoughts, it is all their ruses. No one can scheme deeper than them!
Malbim: They finished searching, and did not find any revealed sin in David. They now seek sin in his heart and conscience; they say that his thoughts are evil.