WEBSTER, N.Y. - The neighbor of a convicted felon who ambushed firefighters on Christmas Eve, killing two, bought the guns for him and lied to the seller, knowing that he wasn't allowed to have them, authorities said Friday.

William Spengler had picked out the semiautomatic rifle and shotgun used in the ambush and went to the sporting goods store with the neighbor when she bought them for him, U.S. Attorney William Hochul said.

The neighbor, Dawn Nguyen of Rochester, was arrested Friday. She faces a federal charge of knowingly making a false statement for signing a form indicating she would be the legal owner of the guns, Hochul said. She also was charged with a state count of filing a falsified business record, State Police Senior Investigator James Newell said.

Nguyen told the Associated Press that she didn't want to talk about Spengler.

The charges stem from the purchase of an AR-15 semiautomatic rifle and a 12-gauge shotgun that Spengler had with him Monday when firefighters Michael Chiapperini and Tomasz Kaczowka were gunned down. Three other people were wounded before Spengler, 62, killed himself. Police used the serial numbers on the rifle and shotgun, which were purchased on June 6, 2010, to trace them to Nguyen, Hochul said.