Answer by taking a quote from the following article:

Duterte was born on March 28, 1945, in Maasin. His maternal grandfather was a Chinese immigrant from Xiamen, Fujian. His father was Vicente G. Duterte (1911-1968), a Cebuano lawyer, and his mother, Soledad Duterte (nee Roa; 1916-2012), was a school teacher from Cabadbaran, Agusan and a civic leader of Maranao descent. Duterte's father was mayor of Danao, Cebu, and subsequently the provincial governor of (the then-undivided) Davao province.

After the 1986 People Power Revolution, Duterte was appointed officer-in-charge vice mayor by president Corazon Aquino. In 1988, he ran for mayor and won, serving until 1998. He set a precedent by designating deputy mayors that represented the Lumad and Moro peoples in the city government, which was later copied in other parts of the Philippines. In 1998, because he was term-limited to run again for mayor, he ran for the House of Representatives and won as Congressman of the 1st District of Davao City (under the Laban ng Makabayang Masang Pilipino coalition). In 2001, he ran again for mayor in Davao and was again elected for his fourth term. He was re-elected in 2004 and in 2007. In 2013, Davao City sent rescue and medical teams to Tacloban to give aid to the victims of Typhoon Haiyan, locally known in the country as Typhoon Yolanda. Financial assistance was also given to Bohol and Cebu for the earthquake victims. In 2010, he was elected vice mayor, succeeding his daughter, Sara Duterte-Carpio, who was elected as mayor. He has been offered the Interior Secretary post 4 times, by presidents Fidel V. Ramos, Joseph Ejercito Estrada, Gloria Macapagal-Arroyo, and Benigno S. Aquino III but rejected all of them. Duterte also passed the city's Women Development Code, which aims "to uphold the rights of women and the belief in their worth and dignity as human beings". Duterte banned swimsuit competitions in beauty pageants in Davao City. Duterte also gained prominence for supporting the first-ever Gawad Kalinga Village inside a jail facility which is only located in Davao City. It is a home-type jail with ten cottages built inside the compound, which now serve as home for women inmates. Davao has the highest murder rate, the second highest rape rate, and the fourth highest number of index crimes in the country, according to official police data for the years 2010 to 2015. Nevertheless, Duterte claims that the city is one of the world's safest, a narrative that gained currency in the national media, creating a widespread public perception that has been a significant factor in establishing support for his nationwide drug policy. Prostitution in the Philippines is illegal. In Davao, by city ordinance, police ensure that prostitutes have a valid health card, but do not arrest them. In 2010, the Philippine Child Protection Unit stated that Davao was one of the top five areas for child prostitution and sex tourism in the Philippines. Jeanette Ampog, the executive director of Talikala, a Davao-based NGO that helps prostitutes, said in October 2016 that child prostitution had sharply increased over the past two years. She said that children were cheaper and more marketable. Through the support of Duterte, the City Council amended ordinance No. 1627, Series of 1994, to impose a prohibition on selling, serving, drinking, and consuming alcoholic beverages from 01:00 until 08:00 each morning. Executive Order No. 39 was signed by Duterte, reducing the speed limits for all kinds of motor vehicles within the territorial jurisdiction of Davao City in the interest of public safety and order. Duterte also signed Executive Order No. 04, Series of 2013 to impose an order creating the implementing of rules and regulations for the new comprehensive anti-smoking ordinance no. 0367-12, Series of 2012. Davao City's Firecracker Ban was also implemented with ordinance No. 060-02/1406-02, Series of 2002 by the City Council through the support of Duterte. Another known accomplishment was that the City Government of Davao was able to acquire 10 more ambulances for central 911 intended for medical emergencies and 42 new mobile patrol vehicles and motorcycles for the Davao City Police Office (the first and only 9-1-1 emergency telephone number in Asia which is also free of charge). Duterte, through Executive Order No. 24, ordered all shopping malls and commercial centers to install, operate and maintain high end and high definition closed circuit television (CCTV) cameras at all entrance and exit points of their premises. We're the ninth safest city. How do you think I did it? How did I reach that title among the world's safest cities? Kill them all [criminals]. Duterte, who has been dubbed "The Punisher" by Time magazine, has been linked by human rights groups such as Amnesty International and Human Rights Watch to extrajudicial killings of over 1,400 alleged criminals and street children by vigilante death squads. In the April 2009 UN General Assembly of the Human Rights Council, the UN report (Eleventh Session Agenda item 3, par 21) said, "The Mayor of Davao City has done nothing to prevent these killings, and his public comments suggest that he is, in fact, supportive." Human Rights Watch reported that in 2001-2002, Duterte appeared on local television and radio and announced the names of "criminals", some of whom were later executed. In July 2005 at a crime summit at the Manila Hotel, Duterte said, "Summary execution of criminals remains the most effective way to crush kidnapping and illegal drugs". Duterte has denied responsibility for the extrajudicial killings. He has also frequently announced his support for them. According to Reuters, "Duterte's loud approval for hundreds of execution-style killings of drug users and criminals over nearly two decades helped propel him to the highest office of a crime-weary land." In 2009 Duterte said: "If you are doing an illegal activity in my city, if you are a criminal or part of a syndicate that preys on the innocent people of the city, for as long as I am the mayor, you are a legitimate target of assassination." In 2015, Duterte confirmed his links to extrajudicial killings in Davao, and warned that, if elected president, he may kill up to 100,000 criminals. After the said confirmation, Duterte challenged human rights officials to file a case against him if they could provide evidence to his links with vigilante groups. CANNOTANSWER

why did they kill?

to crush kidnapping and illegal drugs