The Guard Recruiting Assistance Program was created in 2005 at a time when the National Guard was short 20,000 troops for its operational goals. A small Alabama contractor, Docupak, which for years had printed the Guard’s promotional fliers, said it could create a finders-fee program to fill the hole. The program encouraged the Guard’s citizen-soldiers, who hold civilian jobs while performing part-time military service, to refer potential recruits they met at work, church, county fairs — anywhere their “sphere of influence” might extend. Soldiers whose referral resulted in a successful recruitment were paid between $2,000 and $7,500.

The Guard rushed out the program with minimal training, under a no-bid contract that the Army later deemed to be illegal. Soldiers said commanders pushed hard for everyone to participate. Over the next seven years, more than 130,000 successful referrals came in.

Under program rules, interaction between a soldier and a potential recruit could be as fleeting as a phone conversation and still count as a legitimate referral, the president of Docupak, Philip Crane, later said in court testimony. Docupak was supposed to police fraud by confirming that recruits knew the soldier who referred them before a payout was made. But it is unclear how carefully the company, which got paid only when soldiers got paid, verified the relationships.

Mr. Crane, through his lawyer, declined to be interviewed.

The National Guard initially hailed the program as a success that bolstered its ranks. But in 2012, an Army audit warned that the program appeared to be rife with fraud — perhaps as much as $100 million worth. The audit was leaked to the media. Senator Claire McCaskill, Democrat of Missouri, and other exasperated members of Congress demanded accountability.

The Army created Task Force Raptor, composed of 200 investigators. Its motto: “Do what has to be done.”

According to affidavits submitted in court proceedings by the task force, investigators believed the fraud worked the same way all over the country: Professional recruiters whose job was to find potential recruits would illegally feed names and Social Security numbers to other soldiers, who would then collect referral payments for recruits they had never met. Soldiers and recruiters would then split the money.