After nearly three weeks of hearing testimony about Mark Foley's inappropriate behavior toward former pages, House investigators appear to be reaching the end of their witness list.

A four-member ethics panel worked into the night Wednesday interviewing a senior aide for House Speaker Dennis Hastert. Ted Van Der Meid, who oversaw the page program for the speaker, testified for more than six hours.

Van Der Meid was part of a small group of staff aides and lawmakers who knew of Foley's too-friendly e-mails sent to a Louisiana teen last fall. The matter was handled quietly as then-Clerk of the House Jeff Trandahl and Rep. John Shimkus, R-Ill., confronted Foley, R-Fla., about his actions and instructed him to stop.

Click here for FOXNews.com's You Decide 2006 coverage.

The panel is investigating whether lawmakers and staff aides acted properly when they learned of Foley's behavior. It is expected to hear Thursday from Tim Kennedy, a more junior Hastert aide who last fall fielded the complaint about Foley from the office of Rep. Rodney Alexander, R-La., the former page's sponsor. Kennedy alerted his supervisor.

Foley abruptly resigned Sept. 29 after being confronted with sexually explicit e-mails — instant messages — sent in 2003 to a former page from Oklahoma.

No lawmaker has acknowledged knowing of sexually graphic e-mails. They surfaced only after news broke about Foley's e-mail to the former Louisiana page. But a small group of lawmakers and top GOP staff aides have known for years of inappropriate messages and rumors of bad behavior by Foley toward pages.

For instance, former top Foley aide Kirk Fordham has told the committee that Hastert's chief of staff, Scott Palmer, knew of earlier incidents involving Foley.

Rather than investigating Foley, the four-member panel is trying to determine who knew about his actions and whether more should have been done to stop him.

The panel may want to know what Van Der Meid knew about earlier incidents regarding Foley. For example, the panel has been asked to look into rumors that several years ago Foley tried to enter the page dorm while drunk, an incident that Fordham has testified about.

Trandahl and Rep. Jim Kolbe, R-Ariz., learned in 2001 or 2002 of an episode in which Foley sent an ex-page inappropriate e-mails. Kolbe has not been contacted by the ethics panel about testifying, spokeswoman Korenna Cline said.

In those instances, Foley's inappropriate behavior with former pages have been handled by a few staff aides and lawmakers, rather than being investigated more fully. Foley's misbehavior did not cease.

The panel is also investigating what other lawmakers knew about Foley and when they knew it.

Majority Leader John Boehner, R-Ohio, and House GOP campaign chairman Tom Reynolds of New York have said they heard from Alexander last spring of the more recent incident involving overly friendly e-mails from Foley to the Louisiana teen. Alexander was concerned about news media inquiries into the matter. Boehner and Reynolds say they talked to Hastert about the topic, but Hastert says he does not recall the conversations.

Separately, Foley's attorney revealed Wednesday that the former congressman is being treated for alcoholism at a facility in Tucson, Ariz. Foley has been in a 30-day treatment program at the Sierra Tucson treatment center since Oct. 1.