MANILA  A witness to the massacre of 57 people in the southern Philippines testified Wednesday that the principal suspect in the case, a town mayor, had shot several of the victims himself and that the mayor’s father, the patriarch of a powerful political clan once allied with President Gloria Macapagal Arroyo, had personally directed his son to carry out several of the killings.

The witness, Rasul Sangki, the vice mayor of Ampatuan, a town in Maguindanao Province, told the court that the suspect, Andal Ampatuan Jr., had killed at least three of the victims and ordered his supporters to shoot others to make sure they were dead. One victim was a journalist begging for his life, Mr. Sangki said. But, he testified, Mr. Ampatuan shot the man with an M-16 rifle.

Mr. Ampatuan, the only person indicted in the massacre so far, pleaded not guilty this month to 41 murder charges against him. In a brief interview with reporters on Wednesday  his first since he was charged  Mr. Ampatuan denied any role in the carnage.

“Allah knows that I am innocent,” he said.

Dante Jimenez, chairman of the watchdog group Volunteers Against Crime and Corruption, called Mr. Sangki’s testimony “very explosive and credible.”