"Three [individuals] remain under the status of suspects," Anna Fadeyeva told RIA Novosti.
The spokeswoman added that charges have been brought against Zaur Dadayev and Anzor Gubashev detained earlier in the week.
One of five suspects in the murder investigation of Russian opposition figure Boris Nemtsov claimed on Sunday to have an alibi that absolved him of the assassination.
"At the time of the murder, I was at work as I usually am every day. There are many people, my colleagues, who will confirm this," Tamerlan Eskerkhanov said in Moscow's Basmanny District Court.
Three suspects in the murder of Russian opposition politician Boris Nemtsov pleaded not guilty, a RIA Novosti correspondent reported Sunday from Moscow's Basmanny District Court.
Earlier Sunday, Russia's Investigative Committee was requesting permission to arrest five people involved in Nemtsov's murder.
Nemtsov, 55, who once held high positions in the Russian government in the late 1990s, was fatally shot in central Moscow late last Friday.
Shortly after the tragedy, Russian President Vladimir Putin ordered the Russian Investigative Committee, the Interior Ministry and the Federal Security Service to set up a joint team to investigate the murder. Investigators have been pursuing several motives behind Nemtsov's murder, including possible links to the Ukrainian crisis, contract killing or business-related disputes.