On Jan. 18 at 8:42 pm, five gunmen came over the back wall of a home in the upper-middle-class Metrogate Silang Estates Village in Cavite province, south of Manila, to find five people having dinner on the veranda. As they searched the five, one of them, a retired U.S. Air Force veteran, apparently made a too-sudden move. In the next instant, according to CCTV footage, the vet was shot dead. The other four were terrorized, brutalized and robbed.

The aftermath of that robbery illustrates both the appeal of Rodrigo Duterte, who in May was elected the Philippines’ president in a landslide, and the likelihood that his promise to execute criminals will end in bitter disappointment.

Nearly five months after that home invasion, what should have been an easily solved case remains open, like far too many cases across the country. Such lawlessness was a major factor in bringing the 71-year-old Mr. Duterte, who will be sworn in June 30, to power.

Part of the problem is that criminality is so ingrained into the Philippine system. Members of the police are often suspected of protecting criminals or participating in the crimes themselves. Mr. Duterte’s pledge to use extrajudicial murder to impose peace and order could mean asking the police to execute their own accomplices or even fellow officers.

It also has very little to do with what’s wrong with the Philippines. Mr. Duterte professes to oppose crime, yet he intends to give Ferdinand Marcos, the strongman who stole billions of dollars from the public coffers while he was in power, a hero’s burial. Mr. Duterte also announced that he will pardon former President Gloria Macapagal Arroyo, who has faced charges of corruption and resided in hospital since 2011. Moreover, his appointed spokesman, Salvador Panelo, was the lawyer for officials accused of killing 58 people, including 34 journalists, in the town of Ampatuan in 2009.