What rights does an innocent bystander have to testify before a grand jury?

"If two persons witness an offense one being an innocent bystander and the other an accomplice who is thereafter imprisoned for his participation the latter has no more right to keep silent than the former. The Government of course has an obligation to protect its citizens from harm. But fear of reprisal offers an immunized prisoner no more dispensation from testifying than it does any innocent bystander without a record." Piemonte v. United States, 367 U.S. 556, 559, n.2, 81 S.Ct. 1720, 1722, n.2, 6 L.Ed.2d 1028.

As a corollary, of course, it gives him no dispensation to commit perjury or to conspire to obstruct justice. See In re Grand Jury Proceedings, 509 F.2d 1349 (5th Cir. 1975); LaTona v. United States, 449 F.2d 121, 122 (8th Cir. 1971).