"Massacre in the South", by Robert Riggs. The best bio I’ve been able to find for Riggs is here:
Robert Riggs was born in Decatur, Illinois in 1896. In 1913, he was a student in the fine arts program at James Milkin University and from 1915 to 1917 he studied at the Art Students League in New York City. Riggs moved to Philadelphia where he worked for N.W. Ayer & Co. At the onset of WWI, he enlisted with the Red Cross and served as a medic. After the war, he returned to his previous job. Riggs also worked as a freelance artist producing magazine illustrations, as well as paintings and lithographs for advertising purposes. During the 1930s and 1940s, Riggs made separate art prints, which told of his fascination with the circus, boxing and hospital accident wards. His subjects are realistically portrayed, with an unsettling edge, as if they might be slightly manic. Riggs was fairly notorious for his love of snakes, a number of which he kept as pets in his own home. He taught at the Philadelphia College of Art, now called the University of the Arts.He’s not on Wikipedia (yet). More info, about the auction where this picture was sold:
[Philip Desind] also sought out lesser-known artists and those who had fallen out of favor or luck, notably the Philadelphia painter Robert Riggs, who was well-known in the 1930s but was in ill health when Desind found him in the 1960s. Desind personally got Riggs medical help and put him back on his feet with two Capricorn Galleries retrospectives. Among the 10 Riggs works in the Freeman sale is a tempera-on-panel depiction of a girl handing a bouquet to a Mummers captain, titled Flowers for the Gentlemen. It is expected to bring $8,000 to $12,000. Riggs also had a more somber side. His Massacre in the South, depicting a gang of white men gunning down a group of unarmed African Americans leaving what appears to be a church, is expected to bring $6,000 to $8,000 at the auction; his Slave Market Charleston, South Carolina, which illustrated the cover of the Sept. 3, 1956, issue of Life magazine, is expected to bring $10,000 to $15,000.I can find no other information about “Massacre”, such as date or who commissioned it, but it’s stylistically similar to Slave Market so I guess it also dates from the mid-50s.