[5] The silver-mine owners responded by hiring Pinkertons and the Thiel Detective Agency agents to infiltrate the union and report on strike activity.

[5] An undercover Pinkerton agent, soon-to-be well-known lawman, Charlie Siringo, had worked in the Gem Mine as a shoveler.

Siringo found the "leaders of the Coeur d'Alene unions to be, as a rule, a vicious, heartless gang of anarchists.

Siringo apologized for his work spying on Colorado coal miners, but he never regretted his informant role in the Coeur d'Alene.

"[11][10] Siringo promptly began to report all union business to his employers, allowing the mine owners to outmaneuver the miners on a number of occasions.

Strikers planned to attack a train of incoming replacement workers, so the mine owners dropped them off in an unexpected location.

[14] The guards and strikebreakers inside the mine and mill buildings were prepared for a long standoff, having been warned by Charlie Siringo.

After three and a half hours of gunfire without casualties, striking miners on the hill above sent a bundle of dynamite down a sluice into the mill, destroying the building and crushing one of the strikebreakers.

At the end of the day, six men were dead, three on each side, and there were 150 strikebreakers and guards held prisoner in the union hall.

The Bunker Hill management was taken by surprise, and the strikers took possession of the ore mill during the night, and put a ton of explosive beneath it.

[14] While these men waited to board a boat at Coeur d'Alene Lake, some striking miners fired again, and at least seventeen non-union workers were wounded.

[5] The miners considered the battle over and the union issued a statement deploring "the unfortunate affair at Gem and Frisco.

[5] The governor declared Martial Law,[17] and ordered in six companies of the Idaho National Guard to "suppress insurrection and violence."

13 After the Guard and federal troops secured the area, Siringo came out of the mountains to identify union leaders, and those who had participated in the attacks on the Gem and Frisco mines.

He wrote that "As I knew all the agitators and union leaders, I was kept busy for the next week or so putting unruly cattle in the 'bull pen', a large stockade with a frame building in the center, for them to sleep and eat in."

Many years later, WFM Secretary-Treasurer Bill Haywood stated at a convention of the United Mine Workers of America that the Western Federation of Miners: ...are not ashamed of having been born in jail, because many great things and many good things have emanated from prison cells.Charlie Siringo was not the only agent to have infiltrated the Coeur d'Alene miners' unions.

In his book Big Trouble, author J. Anthony Lukas mentions that Thiel Operative 53 had also infiltrated, and had been the union secretary at Wardner.