The jamming involved more than 800 computer-generated calls and lasted for about 1 1/2 hours on Nov. 5, 2002, the day voters decided several races, including a close Senate contest between outgoing Gov. Jeanne Shaheen and GOP Rep. John E. Sununu, who won by fewer than 20,000 votes.
The lines that were jammed were set up so voters could call for rides to the polls. Democrats say the jamming was an organized, statewide effort that may have even affected the outcome of some local races.
"There is, short of murder, not much that is more horrific in America than purposely trying to stop people from voting," said Raymond Buckley, vice chairman of the state Democratic Party. "I do not believe this investigation should stop until every single person who had knowledge of this and paid for this is prosecuted."
Allen Raymond, former president of the Virginia-based GOP Marketplace, pleaded guilty Wednesday in federal court to conspiring to make harassing phone calls. The charge carries up to five years in prison. He will be sentenced in November.
The Justice Department said the investigation continues.
Republicans acknowledged last year that they hired GOP Marketplace for telemarketing services in 2002. But Republican Chairwoman Jayne Millerick has maintained the company was paid $15,600 for telemarketing services to encourage people to vote Republican, not to jam lines.
Chuck McGee, executive director of the state Republican Party at the time, resigned after news of the jamming broke.
"These allegations have been extremely troubling and we are happy that it appears they are coming to a just conclusion," Millerick said.