A Brooklyn man who beat a transgender woman to death after he had started flirting with her was sentenced to 12 years in prison on Tuesday, a penalty the victim’s family said was too light.

The man, James Dixon, 25, pleaded guilty to manslaughter this month in State Supreme Court in Manhattan, admitting he attacked the woman, Islan Nettles, on a street in Harlem just after midnight on Aug. 17, 2013, knocking her to the pavement with a punch, then hitting her again as she lay on the sidewalk.

Image Islan Nettles

Ms. Nettles, 21, an assistant at a fashion company, died five days later of head injuries, prompting vigils and protests by transgender people who said her death was emblematic of the violence they often face because of their sexual identity.