Two Roxbury men were found guilty Friday in Suffolk Superior Court of the 2011 shooting death of 25-year-old Derrick Barnes, according to the office of Suffolk District Attorney Daniel F. Conley. Frederick Henderson and Frankie Herndon, both 29, were convicted of first-degree murder and unlawful possession of a firearm. They had approached Barnes on Aug. 27, 2011, as he sat on his porch on Fayston Street in Dorchester . Following a verbal altercation, the men shot Barnes, who was pronounced dead at Boston Medical Center, said Jake Wark, a spokesman for Conley.Haven Orecchio-Egresitz can be reached at Haven.Egresitz@globe.com. Follow her on Twitter @HavenTaylor.