These Americans remain imprisoned in Russia. Here are their cases.

What happened: CBS reports that as many as 10 other Americans, including some with dual Russian nationality, remain in Russian custody after Stephen Hubbard's release following more than four years in prison. Key numbers: Hubbard is 74. Why it matters: Russian authorities tightly control information, so detainees' circumstances can be hard to verify. Leake's family said he was left behind in an August prisoner exchange that brought home three other U.S. nationals.

CBS reports that as many as 10 other Americans, including some with dual Russian nationality, remain in Russian custody after Stephen Hubbard's release following more than four years in prison.

Russian authorities tightly control information, so detainees' circumstances can be hard to verify. Leake's family said he was left behind in an August prisoner exchange that brought home three other U.S. nationals.