Police have arrested a third suspect in the January murder of a Roswell grocery store owner.

Joel Augusto Boyce Douglas, 25, was cornered at a southwest Atlanta residence early Sunday morning by members of Fulton County's S.W.A.T. team. Douglas surrendered after a one-hour standoff, six months and a day since Lydia Alvarado was gunned down.

The 39-year-old mother of two was killed after three gunmen entered the Azteca Grocery on Alpharetta Highway. Investigators initially speculated that the suspects knew Alvarado because none of the other employees or customers in the store at the time were harmed.

"It looks now that robbery was their motive," said Roswell Police spokesman James McGee. "[The victim] had a lot of money coming into that store."

All three suspects are native Panamanians. Samuel Alfonso Boyce, 30, of Douglasville, was arrested on unrelated charges last month in Clayton County, where he is still being held.

On Wednesday, authorities tracked down David Alberto Luna, 31, in DeKalb County.

All three are charged with felony murder, armed robbery, aggravated assault and false imprisonment.