'They remain in torturous conditions. They are in grave danger,' says Russian opposition leader

U.S.-Russian prisoner swap saw eight Russians -- including a convicted assassin and spies -- returned to Moscow from Western custody.

But several other Americans that Washington has designated as unjustly imprisoned and political prisoners remain behind bars in Russia .

Nearly 800 Russians designated as political prisoners by the venerable Russian rights group Memorial remain incarcerated by Putin ’s government.

The Wall Street Journal reporter Evan Gershkovich said it was great to see that Russian political prisoners were released.

Relatives and loved ones of U.S. citizens who remain imprisoned in Russia expressed anger and disappointment that they were not included in the prisoner swap.

"This is absolutely unfair that they did not bring him home," Fogel ’s sister, Anne Fogel , told PBS News .

The boyfriend of Karelina 's girlfriend said he was happy for the three Americans freed in the swap, which he said “makes me hopeful” Belarusian opposition leader Svyatlana Tsikhanouskaya also called on the global community not to forget political prisoners incarcerated by the regime.