Lapid is taking the stand for Case 1000, in which Netanyahu is alleged to have received expensive gifts from Israeli businessman Arnon Milchan.
Milchan is accused under Case 1000 of giving expensive gifts to the Netanyahu family in return for aid in obtaining a US visa.
Harow faced fraud and breach of trust charges, but made a plea bargain to testify against his former boss.
For years, as it has appeared sources in law enforcement were leaking stories against him in the media, Harow mostly held his fire.
The American-born Harow testified in relation to Case 2000, which alleges that Netanyahu sought to weaken a competitor of a paper in return for positive coverage.
Case 1000, a corruption trial in which Netanyahu is charged with fraud and breach of trust, resumed on Monday.
List of witnesses in PM's Case 1000 significantly shortened, KAN News reported, adding that A-G Gali Bahrav-Miara could mediate in hopes of a plea deal.
Barak added that he was “dumbfounded” that Netanyahu suddenly abandoned talks on a plea deal.
The Movement for Quality Government NGO petitioned the High Court, calling to limit Netanyahu's Prime Ministerial powers.