MANILA, Philippines—Senator Miriam Defensor-Santiago on Thursday asked Justice Secretary Raul Gonzalez for an immediate investigation of the killing of her aunt in Iloilo City.

In a "rush and personal" letter dated August 28, Satiago requested Gonzalez to direct National Bureau of Investigation Director Nestor Mantaring and Iloilo Regional Director Mario Sison “to investigate immediately” the murder of Adelina Bermejo.

Santiago said she believes her aunt, a retired nurse and a balikbayan from the United States, was killed for her US pension.

"I believed that she was alone and defenseless when she was stabbed in the back. Presumably, the motive was theft, because of her pension," she said.

Bermejo, 74, was found dead Thursday morning in her residence in Jaro, Iloilo, in one of the duplex house she shares with her son, Dr. Adino Bermejo of Iloilo Doctors Hospital.

Santiago said that before her murder, a neighbor reportedly heard her say: "Come in, Robert." She said Robert is the name of the houseboy of Bermejo's sister Liberty and he was sometimes sent on errands to the victim's house.