Jim Tomsheck, the former head of Customs and Border Patrol internal affairs, speaks during an interview with The Associated Press, Wednesday, Dec. 21, 2016, in Washington. Tomsheck says that when he was CBP’s chief of internal affairs from 2006 to 2014, about 30 applicants admitted during the lie detector test that they were sent by drug cartels; one said he killed his infant son. (AP Photo/Evan Vucci)

Jim Tomsheck, the former head of Customs and Border Patrol internal affairs, speaks during an interview with The Associated Press, Wednesday, Dec. 21, 2016, in Washington. Tomsheck says that when he was CBP’s chief of internal affairs from 2006 to 2014, about 30 applicants admitted during the lie detector test that they were sent by drug cartels; one said he killed his infant son. (AP Photo/Evan Vucci)

SAN DIEGO (AP) — When James Tomsheck joined U.S. Customs and Border Protection in 2006 as chief of internal affairs, the nation’s largest law enforcement agency was on an unprecedented hiring spree.

The Border Patrol, a part of CBP, held job fairs across the country, aired recruitment ads during Dallas Cowboys games and sponsored a NASCAR race car and bull-riding contests. The agency ballooned by nearly 8,000 agents in three years to more than 20,000 in 2009.

But breakneck growth brought unintended consequences that serve as a cautionary tale to President-elect Donald Trump and others who want more agents.

The number of employees arrested for misconduct, such as civil rights violations or off-duty crimes like domestic violence, grew each year between 2007 and 2012, reaching 336, a 44 percent increase. Additionally, more than 100 employees were arrested or charged with corruption during the six-year span, including taking bribes to smuggle drugs or people.

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“I came to clearly understand in 2008 that the hiring initiative had gone awry and there were significant problems,” Tomsheck said.

Tomsheck helped introduce lie detectors in Secret Service hiring in the 1980s and forcefully argued for the same at CBP. President Barack Obama signed legislation to make polygraphs a CBP hiring requirement, and Tomsheck put the practice in place for all hires in 2012.

But now, CBP’s high failure rate among applicants taking lie detectors has left the agency unable to fill jobs, and some members of Congress and union officials believe qualified people are being unfairly subjected to marathon and often-hostile interrogations.

However, a panel of law enforcement experts appointed by Homeland Security Secretary Jeh Johnson to review CBP last year called the polygraph “an important integrity tool” in hiring and recommended employees be periodically tested, as the FBI does. It called corruption “the Achilles’ heel of border agencies.”

CBP Commissioner Gil Kerlikowske, who leaves office Jan. 20, has a warning for his successors: Be careful in hiring.

“If I was the commissioner (in the 2000s) and they said, ‘Here’s the money from Congress, hurry up and hire people and, look, just get them on board as fast as you can,’ that’s just a huge mistake,” he said.