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Thank you very much for the hints, John!!

An image search pointed me to the following site for Graphomya maculata

http://www.quelestcetanimal.com/tag/muscide/

Too bad I don't know french.

The same species was found in Hongkong too but difficult for me to compare from the lateral view.

http://www.fehd.gov.hk/english/safefood/photo_page2/Muscidae/Graphomya%20maculata.html