City Police looking for robbery suspect who's face is "locked in"

Baltimore police are searching for the person whose picture is on the lock screen of a phone dropped by a robber in Mount Vernon. 
The robbery happened on July 25th in the 800-block of Park Avenue.  A woman was walking in the area when she was approached by three people, one of whom pulled a gun and robbed her.  The robbers left with her purse, but one of the three dropped his cellphone.  Police have released the photo and are asking for help in identifying the person displayed on the device's locked screen.  Anyone with information is asked to contact police.