The incident took place a day after a policeman was sacked and arrested for hitting a woman with a brick.
The deceased have been identified as Shakuntala, 55, Meera, 50, and Maya, 28. Pal was currently posted with PCR Command at the police headquarters.
"We have registered a case under section 304 (A) and the sub inspector has been arrested," said a senior police official. The incident took place near Mehrauli-Badarpur road when six sanitation workers were cleaning the road and the sub inspector hit them at high speed, investigators said.
Eyewitnesses said that all three died on the spot. Pal had night duty at PHQ and was returning home when the incident took place. It is being suspected that he dozed off and lost control over the car when the incident took place.
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