This is the second part of a two-part series. Read part one here.

Americans spent approximately $100 billion a year on illegal drugs between 2000 and 2010, according to a 2012 report published by the RAND corporation. Part of the Drug Enforcement Administration's job, alongside several other law enforcement agencies, is to make that process more difficult at home, where harsh federal drug laws have ensured that such transactions are conducted -- until recently, in some states -- entirely on the black market. The DEA also works to cut off imported illicit drugs at the source, which means mounting operations around the world to tackle a global drug trade that generates $322 billion annually, according to UN estimates.

It's a gargantuan task. Critics of the war on drugs say it's an impossible one. Over 40 years, the U.S. has spent more than $1 trillion in the fight. Thousands of people on both sides of the battle have lost their lives. In the end, it's led only to cheaper, higher quality drugs at home and abroad, and by most accounts, little change in the number of people using them. While the momentum may finally be shifting away from an enforcement-first national drug policy and toward prevention and treatment, aggressive enforcement of the nation's drug laws doesn't appear to be going anywhere just yet.

Until the nation drastically rethinks its approach on drugs, the DEA will continue to play an integral part in the war against them, and that sometimes means resorting to controversial tactics. Below, find out how domestic spying, broken promises and a 14-year-old from Detroit have all played a part in that seemingly endless struggle.

The DEA has been spying on U.S. citizens with a surveillance program more expansive than the NSA's.

Just months after Edward Snowden unmasked the National Security Agency's massive domestic spying program, The New York Times broke news of the Hemisphere Project, which pairs experts from telecommunications giant AT&T with federal and local anti-drug officials, including DEA agents. It gives law enforcement officials access to "every call that passes through an AT&T switch -- not just those made by AT&T customers -- and includes calls dating back 26 years," according to the Times report. That's around 4 billion call records every day, each logged with information on the location of callers. The official government slideshow describing the program suggested it had been helpful in tracking drug dealers who frequently change phones, or use disposable "burner" phones.

The White House attempted to allay privacy concerns about the Hemisphere Project last year, noting that AT&T stores the collected data, unlike in the NSA's program, in which data is turned over to the government. Federal officials can quickly access the records, however, often within an hour of a subpoena.

The ACLU criticized the apparent secrecy of the program, which had been in existence for six years before being revealed by the Times in 2013. The organization suggested that blanket surveillance and close federal involvement could represent a violation of the Fourth Amendment protections against unreasonable search and seizure.

"Hemisphere is deeply troubling, not only because the government is amassing detailed, comprehensive information about people who've done nothing wrong, but also because the government has deliberately kept Hemisphere secret, even from criminal defendants who've been subjected to the program," wrote ACLU attorney Linda Lye.

And the DEA instructs agents not to tell the truth about sources of key intelligence.

A Reuters report, also from 2013, detailed how the DEA's Special Operations Division, or SOD, teaches agents to cover up vital tips that come from the department. A DEA document obtained by Reuters shows that federal agents are trained in "parallel construction," in which essential intelligence obtained SOD wiretaps, informants or other surveillance methods can be concealed by crediting it to another source.

An unnamed former federal agent who received tips from the SOD gave an example of how the process worked: "You'd be told only, 'Be at a certain truck stop at a certain time and look for a certain vehicle.' And so we'd alert the state police to find an excuse to stop that vehicle, and then have a drug dog search it," the agent said.

If an arrest was made, agents were instructed to hide the fact that the initial tip had come from SOD, and instead use "normal investigative techniques to recreate the information." This process is sometimes used to hide case details from prosecutors and judges, as well as defense attorneys. Several lawyers told Reuters that the practice could jeopardize a defendant's constitutional right to fair trial and cover up evidence that might otherwise be inadmissible.

DEA officials defended the technique, however, calling it a common law enforcement tool that allows the SOD to crack high-profile cases.

The DEA has confidential informants who have made it a lifetime career.

Confidential informants -- sometimes referred to as "snitches" -- are crucial assets in the DEA's war on drugs. In 2005, the agency told the Justice Department it has around 4,000 of these sources actively working for it at any given time. Many of these informants are recruited after being caught for drug crimes themselves, and are offered a chance to work for the DEA as a way to earn a reduced sentence. Others have made a full-time profession out of informing, a controversial practice in itself, as some critics suggest it encourages longtime informants to go after and potentially entrap low-level dealers rather than higher profile targets.

Informants can make tens or even hundreds of thousands of dollars helping the government prosecute and convict drug dealers, with payment often contingent on how much money is seized in an eventual bust. That's how Andrew Chambers Jr. once made a name for himself as "the highest-paid snitch in DEA history," with a 16-year career as a federal informant between 1984 and 2000, during which time he reportedly netted as much as $4 million in government money, nearly half of it from the DEA. A report earlier this year in the Pittsburgh Post-Gazette found that Chambers was only one of the agency's million-dollar informants.

Chambers, seen in a YouTube video from the Speakers Agency.

The "highest-paid snitch in DEA history" was also found to have lied repeatedly in testimony. Despite his reputation, he recently resumed work with the DEA.

Chambers' work with the DEA halted in 2000, after a review of testimony revealed he'd committed perjury in at least 16 cases, when he lied on the witness stand about his credentials. Agents who'd worked closely with Chambers during the time, however -- including Michele Leonhart, who became DEA administrator in 2010 -- spoke highly of him despite the criticism that made him a national story. Around the time of Leonhart's confirmation, the DEA reactivated Chambers as an informant.

While his current role with the DEA is unclear, legal professionals have expressed concerns beyond Chambers' record of perjury. Defense attorneys told the Arizona Republic that he regularly failed to record introductory meetings, which left open the possibility that he was entrapping suspects and compromising cases.

Shortly after news broke that Chambers had resumed working with the DEA, a case in which he served as the primary informant fell apart and federal prosecutors asked for the charges to be dismissed.

Confidential informants are given so much free rein that one top DEA source actually had his own sub-network of informants.

While the DEA has released information about the general size of the program and the basic guidelines under which it operates, less is known about exactly how -- and to what extent -- the agency controls its informants.

The perils of this ambiguity were exposed in 2004, when it was revealed that a star DEA informant was actually paying his own sub-informants to help him set up drug deals. In one case, in which this arrangement wasn't initially revealed to defense attorneys, a sub-informant made a number of calls to a defendant who would later be facing charges for trafficking methamphetamines. The calls weren't recorded, however, which opened up the possibility that the alleged meth trafficker had actually been pressured to go through with the deal that led to his arrest. A judge determined that this raised the possibility of entrapment and ordered federal prosecutors to release a full list of the cases in which the informant and sub-informant had collaborated. When the government refused, the judge threw out the indictment and freed the defendant, writing that the DEA had tried to "shield itself from accountability by hiring someone outside of law enforcement who is free to violate citizens' rights."

In a ruling explaining her decision, the judge also blasted the DEA, suggesting it was "highly unlikely" that it was unaware of the informant's sub-contractors. In an earlier case, the informant had testified that he'd never told his DEA handlers about his network, and that they'd never asked.

The DEA allows informants to break the law, but have no records as to how often it happens.

Federal agencies came under fire in 2012 in the wake of the Fast and Furious gun-walking scandal for not adequately tracking instances in which they authorize informants to commit crimes in the line of government duty. In the case of Fast and Furious, gun dealers working with the Bureau of Alcohol, Tobacco, Firearms and Explosives sold 2,000 weapons to Mexican cartels, but failed to have them traced. In response to a USA Today report, both the ATF and DEA claimed they were "in compliance" with rules determining when they could advise their informants to break the law.

Both agencies also acknowledged that they didn't track how frequently they granted such permission.

Some congressional representatives have called for more accountability among federal agencies with regard to informants. Rep. Stephen Lynch (D-Mass.) sponsored an unsuccessful bill in 2013 that would have required federal agencies to report to lawmakers whenever an informant commits a serious crime, with or without authorization.

One of America's most notorious terrorists once served as a DEA informant.

In 2013, David Coleman Headley, an American of Pakistani descent, was sentenced to 35 years in prison for plotting the 2008 Mumbai terrorist attacks, which killed at least 164 people and wounded hundreds more. Government officials with knowledge of Headley's past spoke of a man who had grown increasingly radicalized in the years leading up to the attack, but subsequent reporting also followed up on his work as a confidential informant for the DEA between 1997 and 2005, according to sources.

The DEA, which sent Headley on a number of trips to gather intelligence on heroin traffickers in Pakistan, has denied that he was working officially with the agency as late as 2005, or at any time when he was receiving training at militant camps in the region.

An Indian soldier takes cover as the Taj Mahal hotel burns during gun battle between Indian military and militants in Mumbai, India. (AP Photo/David Guttenfelder, File)

Another informant allegedly shot and killed a man who confronted him for molesting his child.

Sometimes informants get caught doing unauthorized dirty deeds while on the agency's payroll. In Albuquerque, the DEA is facing a lawsuit claiming it was negligent in supervising an informant who allegedly shot and killed another man earlier this year. The informant has been charged in the man's death, as well as with criminal sexual penetration of a child under 13 and a host of other charges. The victim had allegedly confronted the informant over the sexual assault of his son when he was shot. The suit is seeking $50 million in damages, alleging that the informant had prior felony convictions and a history of violence and should not have been recruited by the DEA.

The DEA strung one informant along for 20 years with the promise of citizenship. She still hasn't received it.

When Norma was just 19 years old, she became a confidential informant for the DEA. She told her story to Yolanda Gonzalez Gomez as part of a partnership between New America Media and HuffPost Voces. Norma explained how desperation and the promise of citizenship led her to sign up for a commitment she knew little about. Over the course of 20 years, Norma says she repeatedly put her life on the line for the DEA, and in return, she got paid, although she said agents sometimes refused to give her the money she was owed. Citizenship, however, never came, and now Norma fears she'll be deported and sent back to Mexico, where she hasn't lived since she was 5 years old. She also said she believes her life would be in danger there as a result of her work for the DEA.

Norma is an alias -- she asked that her real name be withheld -- but immigration attorney Jodi Goodwin knows stories like hers are not uncommon. "Federal government agencies use and abuse undocumented confidential informants for years, trample their rights with impunity, promise them permanent residency and never deliver on it," she told Gomez. "And they know they don't have to deliver on it. But they keep pressuring them with that promise so they will keep cooperating."

The DEA has also been accused of using other exploitative means to recruit assets.

In a lawsuit filed earlier this year, a New Mexico man and former DEA informant alleged that the agency had recruited him by targeting his history of substance abuse. An attorney representing 38-year-old Aaron Romero claimed that her client had recently beaten a crack cocaine addiction in 2011, when a DEA-sponsored informant offered him the opportunity to sell drugs -- provided to him by the U.S. government -- and to feed the agency information on other drug dealers. His payment, Romero's attorney alleged, came in the form of crack for personal use. Romero relapsed, his attorney said, and was eventually arrested on federal counts of distributing crack cocaine near a school, charges that were ultimately dropped after he spent a number of months in jail.

The DEA once turned a teenager into a drug kingpin so he could act as an informant.

In the 1980s, federal agents with the DEA and FBI plucked 14-year-old Richard Wershe from his Detroit high school and began crafting a new identity for him as a drug kingpin. Over the next few years, the teenage Wershe would live a double life, one as the legend who'd later be known as White Boy Rick, one of the most notorious drug lords in city, and the other as a valuable informant for the DEA and other law enforcement agencies.

"I was just a kid when the agents pulled me out of high school in the ninth grade and had me out to 3 in the morning every night," Wershe told The Fix in 2013. "They gave me a fake ID when I was 15 that said I was 21 so I could travel to Vegas and to Miami to do drug deals."

With intelligence provided by Wershe, authorities were able to make a series of high-profile arrests, disrupting Detroit's rampant drug trade and the police corruption that had grown alongside it.

But in 1988, then 17 and no longer an informant, Wershe was pulled over and busted for work in the same drug business as the one to which the DEA had introduced him. The 17 pounds of cocaine found in his car resulted in a life sentence. He's the only convict still behind bars in Michigan to receive a life sentence as a minor under the state's now-repealed "650-lifer" law. Many of the targets whom Wershe helped put in jail have long since been released.

The DEA did treat one informant very nicely, giving him nearly $900,000 for information it could have gotten for free.