Raul Segura-Rodriguez will go before a judge Thursday.
Segura-Rodriguez and Augustin Toscano were arrested in February following a police chase.
Police say they bound the hands of three people in an apartment on North Winthrop Avenue and then cut their throats. Two of the victims died.
Sources said the suspects were drug dealers who robbed and killed their customers.
On Wednesday night, Segura-Rodriguez was charged with four additional counts of first-degree murder for the deaths of four people in a garage on South Kildare Avenue in September.