The man, an M.Tech graduate from Himachal Pradesh and looking for a job here, had been arrested, they said.
Police said the two got into argument over money and when the woman threatened the man with a knife, he snatched it and stabbed her in the early hours.
On hearing about the commotion, neighbours alerted the police following which they rushed to the spot.
By then a few people of African origin who had gathered at the spot shouted against the police and raised slogans "we want justice".
One person of African origin had been taken into custody for allegedly misbehaving and trying to attack the police personnel, they added.
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