SAN FRANCISCO — The last time Silicon Valley was booming, the U.S. attorney’s office was in hot pursuit.

With Robert Mueller at the helm of the office from 1998 to 2001, a specialized team aggressively targeted corporate wrongdoing and insider trading fueled by the dot-com bubble. But with money coursing through the Valley once more, there’s been a curious quiet from U.S. Attorney Melinda Haag.