Federal prosecutors in Massachusetts, where the death penalty was abolished nearly 30 years ago, face the rare prospect of two simultaneous capital cases for unrelated killings that happened more than a decade apart.

Prosecutors under the direction of U.S. Attorney Carmen Ortiz in Boston have a Jan. 31 deadline to announce whether the government will seek to execute Dzhokhar Tsarnaev, jailed for his alleged role in carrying out the attack at the Boston marathon in April.