I don’t remember the plot very well but it’s stuck in my head for a while. I only recall some details which I will list below 
An Investigation Is Going On About Recent Murders. All The Suspects Die While Having A mysterious Smile On Their Faces. The Smile On The Dead Bodies Is Due To a needle places in accupressure point on their armpits. All the deaths are related to one girl. They were her suitors. Prime suspect is her sister. As far as I remember it was a Chinese movie but it could be other ethnicity as well. It is released around 2010s
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Just a wild guess, maybe?:
“Kiss of the Dragon” (2001)
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Another very wild guess, probably not the right movie, but there are acupuncture and needles in this one, maybe?:
“Golden Needles” (1974)
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