United States government is reportedly considering imposing a visa ban or financial sanctions against Mrs. Diezani Alison-Madueke, ex-petroleum minister, and a dozen of her associates, government officials in the oil and gas sector and politicians.

Quoting US officials, The Wall Street Journal (WSJ) reported yesterday that Washington was scrutinising whether Alison-Madueke’s associates laundered money in the US, United Kingdom and other countries.

In the report, The Wall Street Journal said the UK and US have thrown their muscle behind Buhari’s bid to recover billions of dollars he alleges his compatriots embezzled and stashed abroad.

However, at stake is whether courtrooms thousands of miles from Africa can help the continent track down stolen money, seize it, try the culprits and return the funds in a timely fashion.

In May, Buhari became the first Nigerian to unseat an incumbent president, elected on his vow to recover a vast fortune of money lost to corruption. Within weeks, he was at the White House to ask for help.

“We’re all in,” replied Vice-President Joe Biden, said Garba Shehu, spokesman of the president.

When it comes to helping Africa’s top economy battle graft, this month has offered the first glimpse of how fast and far Buhari’s friends abroad can move.

According to WSJ, in the past, Western governments have acted on similar pleas from other African states—but this time, they have operated with unprecedented nimbleness.

Following a summer meeting in Washington between British and American investigators, London police on October 2 raided a luxurious home near Regent’s Park. There they briefly detained Alison-Madueke, oil minister from 2010 to 2015.

Hours later, her neighbours in Nigeria watched as scores of cops searched her house: “The former minister has questions to answer,” said Bitrus Babuje, a fellow resident of the leafy Abuja suburb called Asokoro.

One of Africa’s most prominent politicians, Alison-Madueke and her associates are suspected of bribery, corruption and laundering money through British and US banks. She has previously denied those allegations and police haven’t charged her with anything.

A lawyer speaking on her behalf, Oscar Onwudiwe, said she was invited by the police in London this month but not arrested. He said he didn’t know the purpose of the invitation. “If the police come to your house for any reason, does it make you a criminal?” he told WSJ.

For the federal government, the detention announces Buhari’s intent to root out endemic corruption, a promise at the core of his campaign. Eventually, the crackdown could help recover the much-needed funds for an exchequer hit hard by collapsing oil prices.

“Most of the money taken out of Nigeria is taken to the West,” said Femi Adesina, a spokesman for Buhari. “So Nigeria will need collaboration with the West.”

Nigeria isn’t the first African country to find its officials investigated abroad for financial crimes. But the current flurry of legal action seems unique for its speed and scope. Buhari is president of Africa’s most populous state—and he has leveraged that position to steer a global hunt for laundered money.

Anticorruption investigators in Nigeria have arrested three directors at the state oil company – Nigerian National Petroleum Corporation (NNPC) – in recent days, said two people close to the administration. None were charged; the oil company says it is eager to expose corrupt employees.

American officials have also considered a visa ban or financial sanctions against Alison-Madueke and a dozen of her associates, oil officials and politicians, US officials said. Washington is scrutinising whether her associates laundered money in the US, the UK and other countries, the officials said.

Both the US State Department and the UK’s National Crime Agency (NCA) declined to comment on their investigations: “We continue to work with Nigeria to fight corruption,” a State Department official said.

Together, the litany of legal actions—conducted on three continents— point to a swift but uncertain precedent for Africa’s struggle against corruption.

“The real issue is the signalling effect: that holding public office in Nigeria should not be a licence to plunder,” said Bismarck Rewane, Managing Director of Lagos research firm Financial Derivatives Company. “It’s working. The number of bribes I’m being asked for has dropped.”

For the better part of a decade, graft fighters in Africa, having lost faith in their own courts, have asked judges in Europe and America to wage their battles.

Major political figures in Gabon, Equatorial Guinea, and Republic of Congo have all seen their assets frozen or targeted by French or American courts.

But those investigations have proceeded slowly. In some cases, they have stalled. Prosecutors have struggled to prove that cars, houses, and artwork there were purchased with money stolen thousands of miles away.

For now, a civil court in West London has frozen £27,000 ($41,400) confiscated by the police from Alison-Madueke, said a clerk at the court. Police also seized £5,000 and $2,000 from her mother, court clerks added. The small amount is the first publicly recorded evidence that legal action has been taken against the former minister and her family.

Buhari has also been in London lately: He met with Prime Minister David Cameron at his Downing Street office in May.

On the flight there, he sat in British Airways’ first class—just a few rows in front of Alison-Madueke—said two people familiar with the matter. The president-elect at the time refused to speak to her, they said, for the entire six-hour flight.