20-year-old Michael Thomas and 23-year-old Keifer C. Wright were shot Monday afternoon inside the Harbor Club Apartments.
Thomas was pronounced dead a short time after and Wright succumbed to his injuries days later.
Police arrested 21-year-old Christie Emmons Thursday morning without incident in connection to the crime.
The first two suspects 20-year-old Paul Lacombe and 24-year-old Elijah Pressley were arrested Wednesday in Delaware.
The investigation so far revealed that the suspects conspired to rob the victims.
Emmons and Pressley both face conspiracy and attempted robbery charges.
Lacombe is accused of shooting the victims during the robbery attempt and faces murder charges.
Pressley and Lacombe both remain at the Howard Young Correctional Institute and Emmons remains at Baylor Women's Correctional Institution.