An Indian couple was brutally slain in the northern state of Uttar Pradesh on Thursday after a heated argument with their grocer, according to a CNN report.

The couple, Bharat and Mamta—who belonged to the lowest social caste in India—were allegedly involved in a dispute with their upper-caste shopkeeper, whom the couple owed 15 rupees (or 22 cents). According to CNN, the couple told the shopkeeper they could not pay the debt, but would bring him the money after they earned their day's wages working in nearby fields. That's when the shopkeeper "went home, grabbed an axe, and attacked the couple." 

"It is not clear yet whether the shopkeeper had some vengeance against the couple," Digambar Kushwaha, a local police official, told CNN

The attacker reportedly confessed his crime to police; Kushwaha says the department is still investigating the attack, and that it is not yet clear what his wife's role in the attack was. Both the shopkeeper and his wife have been arrested, however, and the axe used in the murder was recovered. Bharat and Mamta reportedly leave behind four children, three of whom are minors. 

"We are also probing some eyewitnesses to find out why no one tried to stop the shopkeeper," Kushwaha continued. 

India's prime minister, Narendra Modi, traveled to the U.S. in June to address Congress about forging a stronger security relationship between the two countries. He argued that a stronger partnership between the U.S. and India would increase peace "from Asia to Africa and from the Indian Ocean to the Pacific."