As Afghanistan and Washington deal with the fallout from the assassination of Afghan President Hamid Karzai's powerful half-brother on Tuesday, it's worth reviewing the West's controversial backing of a man repeatedly accused of corruption and dealing drugs.

The killing of Ahmed Wali Karzai, better known in diplomatic circles as AWK, throws into sharp relief the pattern by the West and the Afghan government of relying on problematic powerbrokers and warlords since the fall of the Taliban in late 2001. Also, the assassination has left a major power vacuum in the south, the major stronghold of Taliban-led insurgents and the drug trade, even as the United States plans its withdrawal and endgame for Afghanistan.

Until his brother's rise to power, Ahmed Wali Karzai was best known for the leek dumplings at his Chicago restaurant. Since then, although his official position was simply the head of the Kandahar provincial council, he was much more than that. He was the de facto leader in four of the country's southern provinces. He was accused of dealing drugs, of taking kickbacks in land deals, of interfering in political assignments. Cross Ahmed Wali Karzai, the refrain went, and kiss your government job goodbye. Throughout the south, he was the person to know, the person who determined things as small as where a car dealership could set up shop in Kandahar. Many credited him with securing his brother's re-election in the south in 2009.

Most of the rumors about Ahmed Wali Karzai and the complaints about his fiefdom involved dope. As far back as 2004, there were whispers that he was running drugs out of Kandahar, or at the very least, charging drug runners a massive tax.

Western officials were always ambivalent about AWK and other Afghan officials accused of trafficking drugs. Yet nothing seemed to change the fact that for the West, Ahmed Wali Karzai became the go-to man in southern Afghanistan—in large part, because there was no one else. He was one-stop shopping for getting things done, the devil they knew.

The Karzais dismissed allegations of drugs and corruption as politically motivated. In an interview in his Kandahar compound in June 2006, Ahmed Wali Karzai told me that the claims were an attempt to discredit his brother. "I am sick and tired of the drug accusation," he said. "It's the same old story. It's to get to the president."

But by 2008, the reports had gathered strength. The following year, Gen. David McKiernan, then the top American commander in Afghanistan, allegedly began a push to gather evidence that could tie Ahmed Wali Karzai to the drug trade. In an unrelated move, he was ousted as commander soon after initiating the effort.

Diplomatic cables released by Wikileaks show the increasing suspicions of some U.S. officials. "The meeting with AWK highlights one of our major challenges in Afghanistan: how to fight corruption and connect the people to their government, when the key government officials are themselves corrupt," said a U.S. Embassy report from a meeting in October 2009.

Yet that same month, the New York Times reported that the CIA had been making regular payments to Ahmed Wali Karzai for much of the previous eight years, allegedly for his help in running a paramilitary force and other assistance.

Despite the controversy, dozens of men continued to show up at Ahmed Wali Karzai's compound every day, all eager to pay their respects and ask for favors, the way business has always been done in Afghanistan. On Tuesday, one of those men, a longtime friend from the same tribe and the same village, shot and killed him.

Although the Taliban claimed responsibility, those who knew both men say a personal rivalry is more likely and suggest the assassin was on drugs. Ahmed Wali Karzai, after years of being the strongest man in the region, had also racked up plenty of enemies.

Regardless of who was behind the killing, the insurgents are expected to try to take advantage of the lack of strong leadership in the region. So far, no one is publicly lining up to be the new powerbroker in the south, and no names are being circulated. Who would want the job? More than half the people assassinated in the country since March lived in Kandahar, the U.N. says. Most of Ahmed Wali Karzai's rivals are either in government jobs elsewhere—or, in many cases, dead.

ProPublica intern Lois Beckett contributed to this report.