What I think was going on here was the committee was setting a perjury trap for Michael. The idea was to get Cicci to testify there were buffers, which lulled Michael into saying he was not a killer, that he did not run the mob etc. That would have set up Pentangeli to testify that Michael did do all these things and that HE was the buffer for Cicci. As Tom said this opened Mike up for several counts of Perjury "and a whole lot more." While they probably could never have convicted him of specific crimes, the Senate could have turned over its information to the Justice Dept for prosecution. I also think it may have opened Mike to a contempt of congress citation which carries jail time. In other words, think of it as something similar to nailing Capone for tax evasion.