When federal prosecutors investigate a company, corporate executives tend to react instinctively by “hunkering down.” But a congressional investigation requires the exact opposite behavior, attorney Michael Bopp told an audience on Friday.

“Here on the outside and when I was on the [Capitol] Hill, the general mindset is, ‘Let’s not engage with Hill investigators,’ ” said Bopp, a former chief counsel of the Senate Committee of Homeland Security and Governmental Affairs, and now a partner at Gibson, Dunn & Crutcher.