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The U.S. Attorney’s Office in Delaware is investigating Hunter Biden’s “tax affairs,” President-elect Joe Biden’s son confirmed Wednesday, saying he is taking the matter “very seriously” and is “confident” he handled his affairs “legally and appropriately.”

“I learned yesterday for the first time that the U.S. Attorney’s Office in Delaware advised my legal counsel, also yesterday, that they are investigating my tax affairs,” Hunter Biden said in a statement. “I take this matter very seriously but I am confident that a professional and objective review of these matters will demonstrate that I handled my affairs legally and appropriately, including with the benefit of professional tax advisors.”

A well-placed government source told Fox News that Hunter Biden is a subject/target of the grand jury investigation. According to the source, a "target" means that there is a "high probability that person committed a crime," while a "subject" is someone you "don't know for sure" has committed a crime. 

The source said President-elect Biden is not a subject of any grand jury investigation at this time.

The source also tells Fox News that this investigation was predicated, in part, by Suspicious Activity Reports (SARs) regarding suspicious foreign transactions. 

Another source familiar with the investigation tells Fox News that the SARs were regarding funds from "China and other foreign nations."

A Treasury Department official, who did not comment on the investigation, spoke broadly about SARs, telling Fox News that SARs are filed by financial institutions "if there is something out of the ordinary about a particular transaction." 

The official told Fox News that the mere filing of a SAR does not mean there has been a criminal act, or violation of regulations, but instead, flags that a transaction is "out of the ordinary" for the customer. The official noted, though, that a SAR could be part of a money laundering or tax investigation.

The investigation, according to a source familiar with the matter, began in 2018. 

LAPTOP CONNECTED TO HUNTER BIDEN LINKED TO FBI MONEY LAUNDERING PROBE 

In a separate statement, the Biden-Harris Transition team said: “President-elect Biden is deeply proud of his son, who has fought through difficult challenges, including the vicious personal attacks recent months, only to emerge stronger.”

Two sources familiar with the investigation tell Fox News that the investigation includes looking at the laptop purportedly belonging to Hunter Biden. 

In October, Fox News first reported that the FBI subpoenaed a laptop and hard drive purportedly belonging to Hunter Biden in connection with a money-laundering investigation in late-2019. 

It is unclear, at this point, whether the subpoenas came as part of the U.S. Attorney in Delaware’s investigation into Biden’s tax affairs. It is also unclear whether the FBI money-laundering investigation was ongoing or directly related to Hunter Biden.

One of the documents, obtained by Fox News, was designated as an FBI “Receipt for Property” form, which details the bureau’s interactions with John Paul Mac Isaac, the owner of “The Mac Shop” who reported the laptop’s contents to authorities. 

The document had a “Case ID” section, which was filled in with a hand-written number: 272D-BA-3065729. 

According to multiple officials and the FBI’s website, “272” is the bureau’s classification for money laundering, while “272D” refers to “Money Laundering, Unknown SUA [Specified Unlawful Activity]—White Collar Crime Program,” according to FBI documents. One government official described “272D” as “transnational or blanket.” 

“BA” indicated the case was opened in the FBI’s Baltimore field office, sources said.

The documents stated that the subpoena was carried out in Wilmington, Del., which would fall under the jurisdiction of the FBI’s Baltimore Field Office. 

Another document, obtained by Fox News, was a subpoena sent to Isaac to testify before U.S. District Court for the District of Delaware on Dec. 9, 2019. One page of the subpoena showed what appeared to be serial numbers for a laptop and hard drive taken into possession. 

The subpoena stated that it was requested by Lesley F. Wolf, who, at the time, served as assistant U.S. attorney for the district of Delaware.

Fox News also first reported in October that the FBI was in possession of the laptop in question. 

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The FBI has declined to confirm or deny the existence of an investigation into the laptop or the emails, as is standard practice.

The Justice Department declined to comment on the investigation into Biden's tax affairs. 

Fox News' Jake Gibson contributed to this report.