A Local Legislative Body's Duty to Investigate When Legislative Activities Are Involved

I've written several blog posts about the criminal trials of a Baltimore council member and the former Baltimore mayor, focusing on their successful legislative immunity defenses (1 2 3 4). However, the former mayor was convicted of embezzling $500 in gift cards (no defense to that), and she resigned. According to a Baltimore Sun editorial blog post, yesterday the council member pleaded no contest (effectively admitting guilt) to a campaign finance violation (accepting oversized contributions), which also required no legislative evidence.

Both crimes are minor compared to the many charges these elected officials protected themselves from by preventing their public votes from being placed into evidence.

The Sun editor contends that the council should investigate the charges against the council member, noting that it has the right to try the matter, even when the court does not. He also contends that the council should penalize the council member, at least by taking away her committee chairmanship.

It's worth noting that when local government legislators defend themselves by saying that, constitutionally, evidence of legislative activities may not be presented against them outside their body, they rarely ask their body to investigate the matter, and the body rarely calls for such an investigation.

If the constitution does protect legislators against outside interference, doesn't that place extra duty on the legislative body to police its members? Shouldn't this duty become operative as soon as relevant information becomes available? In other words, when legislative activity is involved, or even asserted, shouldn't the council's investigation go ahead despite what is or may be placed before a court or ethics commission?