MINNEAPOLIS — A woman’s “illegal buying spree” armed a man with the high-powered firearms that he used to kill three Minnesota first responders during a standoff at a home where seven children were inside, federal authorities said Thursday.

The guns bought by Ashley Anne Dyrdahl included three AR-style semiautomatic rifles, including one with a device that doubles the rate of gunfire, and two semiautomatic pistols, court documents said. In addition, investigators found “a stockpile of fully loaded magazines as well as boxes with hundreds of additional rounds of ammunition” in the bedroom Dyrdahl and gunman Shannon Gooden shared, the indictment said.

Ashley Anne Dyrdahl, 35, of Burnsville, conspired with Gooden to illegally supply him with guns even though she knew that he was a convicted felon who could not legally possess them, U.S. Attorney Andrew M. Luger said at a news conference.

Luger, who described the woman as Gooden’s “long-time live-in partner,” said her “illegal buying spree for Gooden demonstrates a reprehensible disregard for public safety and the law, and the consequences of this disregard for public safety are beyond comprehension.”

Dyrdahl was indicted on one count of conspiracy and five counts of making false statements during the purchase of a firearm. Luger said the charges carry maximum potential penalties of 15 years in prison.

She pleaded not guilty at her first appearance in federal court on Thursday, but was allowed to remain free without bail. She did not respond to reporters’ questions as she left the courthouse.

The chief federal defender for Minnesota, Katherian Roe, said her office probably wouldn’t decide about representing Dyrdahl for future proceedings until Friday.

Police Officers Paul Elmstrand and Matthew Ruge, both 27, and firefighter-paramedic Adam Finseth, 40, were slain during the Feb. 18 standoff in the Minneapolis suburb of Burnsville. Their memorial service two weeks ago drew thousands of law enforcement officers, firefighters and paramedics. Sgt. Adam Medlicott, 38, survived being shot while tending to the wounded.

Investigators say Gooden, 38, opened fire without warning after lengthy negotiations, then later killed himself.

Luger said Dyrdahl bought five weapons from two licensed dealers for Gooden, including those that killed the three first responders. The weapons included AR-style rifles and Glock semiautomatic pistols. One of the rifles had a “binary” trigger, which doubled its rate of fire.

The indictment alleges she repeatedly visited gun stores at Gooden’s direction and bought or picked up the specific guns he wanted between September and January, including the two AR-style rifles used in the shootings. The indictment says she signed forms that falsely attested that she was not planning to transfer the guns to a felon.

Court records show Gooden wasn’t legally allowed to have guns because of his 2007 felony assault conviction, and that he had been entangled in a yearslong dispute over his three oldest children. The children in the house were ages 2 to 15 years.

According to the indictment, Dyrdahl cautioned Gooden in a text message about the illegal purchases, “We just gotta make sure we’re smart about all this ya know?”