Legal experts say prosecutors likely have charged Dylann Roof's friend because they want him to testify at the alleged church shooter's trial.

That testimony could help show Roof's alleged acts were premeditated and intentional, which are vital to pursuing a death penalty case.

Roof's friend, Joey Meek, faces federal charges of lying to investigators and concealing information that, if convicted, could land him in prison for years.

Long-time criminal defense attorney Jack Swerling says prosecutors likely have more leverage with Meek now that he is charged. Former U.S. attorney Pete Strom says he expects the government to aggressively pursue any potential witness who could shed light on Roof's case, possibly offering a plea deal or sentence recommendation in exchange for cooperation.