Arthur L. McElwee III, 23, was killed by gun violence in Chester, Pennsylvania, on December 5, 2012. Born October 8, 1989, his death is listed among more than 300 unsolved homicides in the city.

His twin sister, Elena Jo McElwee, has marked her brother’s memory by writing to him on the fifth day of every month since his death; the letters and family mementos underscore the ongoing pain caused by a lack of answers.

The investigation remains open. If anyone knew Arthur or has information about what happened in Chester on or around December 5, 2012, please come forward.