Daniel Medwed, a law professor at Northeastern University, said that dual prosecutions are relatively rare and typically involve high-profile cases that spark public outcry, such as in the case of the Washington, D.C., snipers.

If Tsarnaev is convicted on the federal charges and sentenced to death or life in prison, a state case would be largely symbolic, Medwed said. But even then, a second prosecution can be seen as helping “avenge an injustice,” he said.

“Prosecutors certainly have good grounds for proceeding,” he said.