A criminal investigation into the financial affairs of former US President Donald Trump and his family business has escalated this week.
On Monday, the Supreme Court ordered Mr. Trump to turn over his tax returns and other financial records to New York prosecutors.
The move was a setback for Mr. Trump, who had sought to prevent prosecutors from seeing his files for months.
Records are considered essential to the criminal investigation.
They could be “a pretty big piece of the puzzle,” Daniel R Alonso, former New York and US federal prosecutor, told the BBC.
You might be wondering: what is this criminal investigation and what is the significance of Mr. Trump’s files?
Here we explain what it is.
What is the investigation?
Let’s start with the basics.
This is a criminal investigation conducted by New York State prosecutors.
Cyrus Vance, the Democratic District Attorney for Manhattan, is the lead prosecutor in the investigation.
He and his team are just investigating the possibility of crimes for now.
Mr. Trump, a Republican, has consistently denied wrongdoing and suggested the investigation was politically motivated.
As part of the investigation, Mr. Vance reviews the financial and tax affairs of Mr. Trump and his family business, the Trump Organization.
This is one of two known criminal investigations into Mr. Trump. The other concerns Mr. Trump’s alleged attempts to overturn the results of last November’s presidential election in the state of Georgia.
How did we get here?
The investigation began in 2018, when Mr. Trump was still president.
First, the investigation examined the role of the Trump organization in the quiet payments made during the 2016 presidential campaign to two women who said they had relationships with Mr. Trump.
Michael Cohen – Mr. Trump’s former personal lawyer – was jailed for his role in the regime under federal or state law in 2018.
Meanwhile, Mr. Vance assessed whether the Trump organization violated New York state laws regarding earnings.
So is that all? No, not quite.
Mr. Vance’s investigation has expanded to include other possible crimes.
The New York Times, citing anonymous sources, said Mr. Vance had “examined whether Mr. Trump, his company and his employees committed insurance, tax and banking fraud, among other crimes.”
This is where tax and financial matters come in.
Mr. Vance needs them to establish whether any crimes have been committed.
For months he has been trying to get eight years of personal and corporate tax returns from Mr. Trump.
Last July, the Supreme Court ruled that Mr. Trump’s files could be reviewed by the prosecutor’s office.
But lawyers representing Trump challenged the ruling, suggesting the court brief was “overly broad” and issued in bad faith.
On Monday, the court rejected this argument.
The ruling means Mr. Vance can access the files, allowing him and his team to review them.
“The importance is pretty great,” Alonso said of the decision. “I mean that in the sense that it is important and that there will be a lot of documents. These documents could run into the millions.”
In a succinct statement addressing the decision, Mr Vance said: “The work continues.”
In contrast, Mr. Trump called the investigation a “political witch hunt.”
What could prosecutors learn from tax cases?
The files will give prosecutors a more complete picture of Mr. Trump’s financial affairs.
For example, prosecutors may be able to explore certain investigative theories, request interviews with witnesses, and establish whether state laws have been violated.
In addition to Mr. Trump’s tax returns, accountants’ analysis and their communications with their client could be included in the records tranche, Mr. Alonso said.
“This is all going to be important, given the allegations that exist,” he said.
We know from court documents that Mr. Vance mentioned tax evasion as a hypothetical crime, if evidence is found to support it.
Many wealthy Americans are using loopholes to reduce the amount of tax they are legally required to pay.
But records could be crucial in determining the legality of accounting methods Mr. Trump and his company may have used.
It will take time for investigators to review the files. In light of this, the investigation could continue beyond the end of Mr. Vance’s tenure as elected prosecutor at the end of this year.
So, as you can probably see, a lot remains uncertain.
How bad could this be for Trump?
“This is not a matter to be taken lightly,” Alonso said. “Obviously, this is a substantial investigation.”
At this point, it is not clear whether prosecutors will lay criminal charges against Mr. Trump, his company, or his business partners.
The investigation can lead to nothing.
However, if prosecutors find evidence of wrongdoing, criminal prosecution is possible.
In New York City, certain types of tax evasion can be charged with crimes called felonies, which can lead to long prison terms.
In theory, Mr. Trump could be summoned to court for a criminal trial in New York City, should he be charged.
This result – although theoretical at this point – would seriously compromise Mr. Trump’s chances of a political return.
For now, however, Mr. Trump’s tax records only give Mr. Vance’s office an opportunity to expand its investigation, nothing more.