Two words: "Travel Reports."
Every government official who is sent to "out-of-town" meetings is required to make a travel report soon after arriving from the trip. In this travel report, she states the itinerary for the trip, the time spent on a particular place, the purpose of the meeting, and a liquidation of advances for the trip. She is also required to attach the plane ticket, the boarding pass, the airport terminal stub, and the official receipts for food expenses. This type of paper work is a serious matter attended to normally by government officials, because a mistake in the travel report here and there can spawn a few administrative and criminal cases. A supervisor level official in the government has made enough travel reports in her career to get to that level.
Michaelangelo “Louie” Zuce, the presidential staff officer, who presented an affidavit, stating that 27 COMELEC provincial election supervisors from Mindanao were treated to a dinner in the La Vista residence of the President sometime in January 2004. See PCIJ background article here. Zuce claims that GMA arrived at 9:00 pm after dinner. Baby Pineda, wife of Bong Pineda, introduced the COMELEC officials one by one to the President. The President then asked the COMELEC supervisors to support her in the 2004 presidential elections. Other things happened that night, but at the end of the night, Zuce writes that "While we were living, Mrs. Pineda gave RD Johnny Icaro of Region 4 white envelopes for all of us. When we opened them in the vehicles, we found that each envelope contained P30,000."
Did this happen? Is Zuce a fake? Check the travel reports. They should be in the Finance and Administration office of the COMELEC regions.