When federal prosecutors investigate a com pany, corporate executives tend to react instinctively by hunkering down. But a congressional investigation requires the exact opposite behavior, according to attorney Michael Bopp.

"Here on the outside, and when I was on the Hill, the general mind-set is, ‘Let’s not engage with [Capitol] Hill investigators,’ " said Bopp, a former chief counsel of the Senate Committee on Homeland Security and Governmental Affairs, and now a partner at Gibson, Dunn & Crutcher. But the wiser course, he said, is to cooperate in private with committee investigations and hope that the panel will not drag you into a public hearing to ask more questions.