The middle-aged couple from the lowest Dalit caste in Uttar Pradesh state were on their way to work early when the grocery store owner asked them to pay their 15-rupee debt.
“The shopkeeper demanded money but they pleaded to be able to pay it later. He became enraged and attacked them with an axe,” Arun Kumar, the investigating officer in Mainpuri district, told AFP.
The officer said the couple had bought goods from the shop last week with a promise to pay the 60-year-old owner within a few days.
“Their refusal to pay made him angry and he killed them,” Kumar said.
The owner was arrested soon after the incident and the murder weapon recovered, the officer said.
Hundreds of people are murdered in India each year over sudden provocations, often trivialities.
In 2014, almost 15 percent of the murders in New Delhi were unmotivated, according to police, and were mostly committed by non-criminals acting in a fit of rage.
More than 33,000 people were murdered in India in 2014, according to latest figures released by national criminal records bureau.