Scott Brown (REUTERS/Brian Snyder)

Former Massachusetts senator Scott Brown (R) has run several attack ads criticizing Sen. Jeanne Shaheen (D-N.H.) for failing to secure the U.S.-Mexico border. But as a member of the Senate Homeland Security and Governmental Affairs Committee, he missed all six hearings on border security that he was eligible to attend, records suggest.

Brown was absent from five hearings in 2011 and one in 2010, according to a review of public records and congressional transcripts and video. Of the six, four were full committee hearings and two were meetings of the subcommittee on Disaster Recovery and Intergovernmental Affairs, to which he belonged.

A review of all Homeland Security Committee hearings during the time Brown was senator shows those were the six he could have attended, based on his subcommittee membership.

It is not uncommon for senators to miss committee hearings. Scheduling conflicts, including other committee meetings, can complicate matters. Shaheen has also been criticized for absences from committee meetings.

But Brown's absences from border security hearings are especially notable since he has sought to elevate the issue in the campaign. He has routinely railed against "amnesty" for undocumented immigrants and argued that Shaheen been too soft on border security.

Brown served in the Senate for nearly three years between early 2010 and early 2013. Polls shows he is in a close race against Shaheen. The outcome of the contest could affect which party controls the Senate next year.

The Senate does not keep track of committee attendance. While imperfect, reviewing transcripts and other records to see if lawmakers spoke provides the best assessment of whether they were present or not.

The full committee hearings Brown appeared to miss were mainly centered around assessing and building progress on border security at the local and federal levels. Brown also apparently missed an April 2010 meeting titled "Border Security: Moving beyond the virtual fence."

As border security became a national issue earlier this year amid the influx of unaccompanied minors coming to the United States through the Southern border, Brown made the issue a central focus in his campaign. He's blamed Shaheen for voting "against border security" and "for amnesty." He's also sought to tie Shaheen to President Obama on immigration and border security. Obama is unpopular in New Hampshire, polls show.

In the Senate, Brown was also a member of the Committees on Armed Services, Small Business and Entrepreneurship; and Veterans' Affairs, which do not have jurisdiction over immigration and border security issues.

Shaheen's attendance record in the Senate has also come under scrutiny. The Boston Herald reported last week that the senator missed nearly half of the public hearings held by the Senate Foreign Relations Committee during the last two years, including one in which officials warned of the threat posed by the Islamic State.

When asked about Brown's absences, his campaign spokesman Elizabeth Guyton pointed to comments Brown made in an interview with Boston Herald Radio last week in which he did not directly criticize Shaheen's absences but referenced the serious threat posed by the Islamic State.

Guyton did not respond to several subsequent questions on whether the Brown campaign disputes the absences the records indicate.

"Senators have a tremendous amount of responsibilities there. I knew in my case I was on four committees, two subcommittees, a bunch of caucuses -- and plus I was doing my National Guard duty, so I don’t think there’s ever an expectation to have 100 percent attendance," said Brown in the Boston Herald radio interview.

Shaheen's campaign declined to comment on Brown's attendance record. The New Hampshire Democratic Party last week criticized Brown for missing hearings on border security and terrorism in the Armed Services and and Homeland Security Committees.

Former senator Gordon Humphrey (R-N.H.) and the New Hampshire Republican Party have criticized Shaheen over her absences.

Transcripts or records suggest Brown missed full committee hearings on border security on April 20, 2010; March 30, 2011; April 7, 2011; and May 4, 2011. The records and transcripts of subcommittee suggest he missed border security hearings on March 31, 2011 and June 9, 2011.