These things can get nasty! ATF vs. FBI, fighting over explosives investigations. The division had been that FBI gets it if it involves terrorism; ATF gets it if it doesn't. But drawing that line in the real world is difficult. So with any high profile case, the investigation has to be preceded by the inter-agency battle.
"Glenn A. Fine, the Justice Department's inspector general, reported last year that battles were flaring at crime scenes from Baltimore to Houston, delaying witness interviews and impairing the government's ability to spot trends in bombings."