ATLANTA—Atlanta police on Tuesday arrested a 22-year-old man in the shooting death of a 6-month-old baby a day earlier. Grayson Fleming-Gray was shot just after 2:30 p.m. Monday while riding in a vehicle, police said. Mayor Andre Dickens announced the arrest during a news conference Tuesday afternoon, praising police for their quick work in making an arrest. “They were all over the place asking and looking for clues,” Dickens said. “They worked 24 hours nonstop until they resolved this issue and now a suspect is under arrest.” Atlanta police Chief Rodney Bryant identified the suspect as 22-year-old Dequasie Little. He was found in Decatur and arrested on charges of aggravated assault and felony murder. It wasn’t immediately clear whether he had an attorney who could comment on the charges. “I won’t cheerlead the fact that we were able to apprehend this person in such a short period of time,” Bryant …