President Barack Obama is seen on a jumbotron during his public swearing in ceremony during his Inauguration on Jan. 21, 2013. Interference with a microwave signal may have caused one of the giant screens to fail. (Joe Raedle/Getty Images)

Interference with a microwave signal may have caused a giant video screen set up on the Mall during last week’s inauguration celebration to flicker and fail, said officials charged with broadcasting the speech to thousands. But the source of that interference remains a mystery.

CP Communications, the company charged with delivering the signals to 12 viewing screens on the Mall, said only the unit near the Washington Monument experienced problems. Unfortunately those problems occurred shortly before President Obama took the oath of office, triggering rounds of boos and groans by viewers camped out to watch the festivities.

Tom Sharkoski, CP’s engineering manager for the Mall event and a general manager in its Philadelphia area office, said the screen’s malfunctioning video and audio was not the only problem. Crews in the same area also found themselves unable to communicate on their walkie-talkies during the breakdown, Sharkoski said.

Sharkoski said company officials may never be certain what caused the problem or identify a source of the interference. The company had a dedicated channel for the feed and did not discover any equipment failure, Sharkoski said. “We have not been able to pin it down on what caused the trouble,” he said.

“It absolutely was a heart-in-my-stomach moment, and my heart goes out to all those people, especially those who may have traveled great distances to witness that event,” he said.

A backup plan to shift to an alternate feed from a broadcast source, such as C-SPAN, never went into effect because of the time consumed by troubleshooting, said John Liipfert, a producer for C3 Present, the Austin-based company that produced a number of events for the inauguration and hired CP Communications.

The Presidential Inaugural Committee declined to disclose what it paid C3 Presents.

The company has also produced the White House Easter Egg Roll and Obama’s 2008 election night celebration in Chicago’s Grant Park. It also is known for putting on music events, including Lollapalooza.

Carol Morello contributed to this report.