The Dominican national police took Martinez Peres into custody Tuesday, the same day the another suspect, Eddy Vladimir Feliz Garcia, appeared in court.
Feliz Garcia faces charges of being an accomplice to attempted murder for allegedly driving the shooter to the nightclub where Ortiz was shot. Feliz Garcia's lawyer said his client was not aware of the plot to shoot Ortiz and unwittingly drove the shooter to the club.
Police said the shooter ran away from the scene after the shooting while witnesses tackled Feliz Garcia, who was arrested immediately.
Four other men, including Joel Rodriguez Cruz, Oliver Moises Mirabal Acosta, Reynaldo Rodriguez Valenzuela and Polfirio Allende Deschamps Vazquez, were also arrested.
A seventh suspect, Luis Alfredo Riva Clases, remains at large and authorities have requested that he turn himself in.
Ortiz, 43, was shot in the back Sunday in Santo Domingo. The three-time World Series champion underwent an operation in his native Dominican Republic before the Red Sox chartered a plane to transport him to Boston for a second surgery.
Ortiz's wife, Tiffany Ortiz, said Wednesday that her husband was in the intensive care unit at the Massachusetts General Hospital.
"Yesterday and this morning, David was able to sit up as well as take some steps," she said. "His condition is guarded and he will remain in the ICU for the coming days, but he is making good progress towards recovery.
"My family and I again want to thank everyone for their endless love and well wishes, and still ask for privacy while David continues to heal."