A day after a former police officer involved with drugs went on a killing spree in Thailand that left two dozen preschoolers dead, calls are mounting for a national crackdown on the cartels that traffic billions of dollars of illicit substances a year.

Former Prime Minister Thaksin Shinawatra urged the government to "speed up the suppression of drugs, especially methamphetamine tablets.” The former prime minister, who is in self-imposed exile, led a yearslong anti-drugs war in the early 2000s in which about 2,500 people were killed.

The perpetrator of Thursday’s massacre, Panya Kamrab, had been dismissed from the police force after being arrested for illegal possession of drugs in January. He was due to attend court on Friday. Thirty-six people died in the knife and gun attack that started at a day care center in Nong Bua Lamphu province, near the Laos border, before he took his own life.