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MANILA - Retired Supreme Court Senior Associate Justice Antonio Carpio on Monday said it was sad that President Rodrigo Duterte backed out of a debate challenged he posted himself because this could have been an opportunity to inform the public about the issue on the West Philippine Sea.

Duterte dared Carpio to debate with him on who was responsible for losing parts of the resource-rich waterway to China. After Carpio accepted the challenge, his spokesman said the President was dissuaded from engaging in it because this might supposedly compromise national policies and confidential information.

• Duterte backs out of debate with Carpio on West PH Sea, pushes Roque as proxy

"I was looking forward to a debate with him because this is the best opportunity to explain the issue to the public. Everybody will be glued to their television, to their computer monitors to watch it. It’s the best way for me to explain the issue to the public," Carpio told ANC's Headstart.

"I’m sad that he withdrew, but that’s his privilege," he said.

Asked about insults Duterte hurled at him and former Foreign Affairs Sec. Albert Del Rosario, Carpio said, "He can call me any names, but I’d rather debate with him on the issues, on the merits."

"Name-calling doesn’t mean anything. Any Tom, Dick, and Harry can call you anything, but nobody can discuss the merits unless you know the merits," he said.

Duterte also alleged Carpio and Del Rosario had a hand at the decision to withdraw Philippine Navy ships in the West Philippine Sea. The President said he would resign if he was proven lying.

• Carpio accepts Duterte debate dare on West PH issue, urges President to resign

Carpio reiterated that Duterte was wrong, and "if he's true to his word of honor, he should resign."

Carpio was a Supreme Court associate justice in 2012 when the standoff at the Scarborough Shoal happened. He said he "never attended any meeting of the executive" and all he knew about the situation were the information reported in the news.

"I had no inside information what’s happening. I did not know about the negotiations to withdraw...The entire cabinet of President Aquino will testify that I never participated in any of the discussions. I can prove it," he said.