Why does Elvis take a picture of the Mercedes Benz that drives by Mrs. Earle's house?

After Mrs. Harris describes a man that looks like Kerris, Elvis stays by the house hoping for his return. When he comes back in his car, Elvis takes a picture of it. He wants to see if it was the same car that Jonna Lester saw her husband meet with at the Mayfair Market. When Elvis shows Jonna Lester the pictures, she immediately recognizes both the car and Kerris as the man who gave James a brown paper bag at the market.