This journalist in Malaya suggests that it was a gift from former President Gloria Arroyo:
He has to convince the senator-judges that the money came from somewhere not illegal but neither is it earned.
Is there such kind of money? Maybe there is! In fact, we have long heard two peers of the Chief Justice, one was then Head Magistrate, the other a retired associate justice from the province of Batangas, saying that he was keeping some money for President Arroyo.
Article link: Whose dollars are those?