(CNN) In the Fall of 2018, Hunter Biden received a quick succession of emails from his accountant: They were all about his taxes.
"They are late," Bill Morgan told his client in October, noting that Biden had missed an already extended deadline of October 15.
"Your 2017 tax returns are still unfiled," the accountant reminded Biden two weeks later.
"You need to get 2017 filed so we can try to work out a payment schedule," he added the following day.
Morgan also noted in that email that Biden's assistant had sent him a copy of an IRS notice from 2015. "They want $158,000," the accountant wrote. "IRS has notified the State Department and they will not renew your passport until this is resolved."
Welcome to the dysfunctional world of Hunter Biden's finances. While the general topic of the President's son's financial troubles has been widely reported, the details surrounding his past filings may offer a glimpse into some of the areas federal investigators are delving into as part of an ongoing probe into possible tax violations and other crimes that is nearing a critical juncture. Prosecutors, sources say, could make a decision soon on whether to file criminal charges against the President's son.
Hunter Biden's legal jeopardy has been leveraged by Republicans seeking to accuse his father, President Joe Biden, of being complicit in his alleged wrongdoing. Republicans expect, should they regain control of the House, to investigate the Biden family through committees they will control.
Biden has denied any wrongdoing and has said he has cooperated with investigators. His father is not implicated in the ongoing federal investigation, according to sources who have been briefed on the matter.
CNN hired a cyber forensics expert to help authenticate a cache of emails related to Hunter Biden's finances that were posted on the internet by a former Trump White House aide and allegedly traced back to a laptop that turned up at a Delaware repair shop.
Information from the laptop has fueled countless stories about Biden's drug abuse, alleged sexual indiscretions and money trouble, many of which CNN -- and other media outlets -- have not been able to verify. Biden has not directly commented on the authenticity of the emails or the stories upon which they are based. He told CBS News last year he did not know if that laptop was his.
Jake Williams, a former National Security Agency operative, who analyzed the emails for CNN, said he was able to authenticate a subset of the emails because they contained verified signatures within their metadata that showed they had not been modified. Only emails he authenticated are cited in this report.
Williams, who previously examined data from the laptop for The Washington Post, said the majority of emails he reviewed for CNN could not be verified because they lacked sufficient technical data necessary for the validation process, among other reasons.
CNN's review of emails showed that Biden struggled with tax issues for years and that his accountant at times seemed at a loss to keep track of the flow of Biden's money. In one email, his accountant raised a question about a $550,000 receipt, asking whether it should be recorded as a loan or income from Burisma, the Ukrainian energy company on whose board Biden served. No response from Biden is shown on that email chain.
Biden received as much as $50,000 a month for serving on Burisma's board from 2014 to 2019, according to a Republican-led Senate report on his business activities.
Despite that lavish income, Biden's debts piled up, even as he received repeated warnings from his bank, his accountant and others.
"Insufficient funds," read an automated Wells Fargo email Biden received in December 2018 that stated one of his accounts lacked $1,700 for a payment on a Porsche. Other bank alerts that year warned that Biden's checking account had a "low balance" and that one of his credit cards had risen above its "pre-set amount" of $65,000.
Attempted charges to another credit card were repeatedly declined due to deficient funds, multiple emails in 2018 and 2019 show.
"I am trying to figure out what to do about bills," Biden's then-assistant emailed him on December 28, 2018. She listed a series of payments Biden owed, including health insurance, a car payment and her salary.
"Pay the health care. Pay the Porsche," Biden responded, though he said she should pay herself half of the salary she said she was owed. Biden also complained that someone else was still getting a cut of what he said he was personally owed by Burisma. "So there's not much income coming through these days," he told her.
By March 2019, Biden's bills, debts and back taxes totaled more than half a million dollars, according to another email from his assistant.
"Please let me know if there is a new plan for paying these bills," the assistant wrote to him in that message, noting he still owed about $370,000 worth of taxes and $120,000 in other bank debt.
Biden's assistant did not respond to multiple requests for comment.
Biden's attorney, Chris Clark, said his client has now "fully paid" his IRS tax debts. Clark added that 2018 and 2019 were difficult times for Biden, who struggled with alcohol and drug addiction after the death of his brother Beau. It is unclear how far back prosecutors may be looking into Biden's tax woes, which according to the emails, date as far back as 2015 and continued into 2019.
"He is current on his tax obligations and is committed to remaining so as he continues his recovery from addiction," Clark said.
During some of the same months that Biden's accountant messaged him about taxes owed, Biden made large cash withdrawals, emails show. He withdrew about $4,800 from ATMs in roughly two weeks in October 2018, for example.
Biden's ex-wife, Kathleen Buhle, wrote a recent memoir chronicling the rockiness of the couple's finances when they were married. "More than once my debit card was declined at a store. I'd have to call Hunter to transfer money into my account," she wrote in her memoir published earlier this year. "Hunter and I drove nice cars and had a beautiful home, but we were running fast on that hamster wheel and barely staying on."
In 2018, Buhle wrote to Morgan, the accountant, who has since died, seeking advice about an IRS tax lien based on an unpaid bill of $112,805.
Buhle said she was at "a loss" and asked Morgan to "Please advise."
In his own book, "Beautiful Things," published last year, Hunter Biden wrote candidly about his addictions. He told NPR he wrote the book to give hope to others who have struggled with substance abuse. He shared that paychecks he received for sitting on the board of the Ukrainian natural gas company Burisma provided him with cash for crack cocaine.
"But by that mad, bad end, the board fee had morphed into a wicked sort of funny money," Biden wrote. "It hounded me to spend recklessly, dangerously, destructively. Humiliatingly. So I did."
He was continuing to make amends, "both figurative and literal," he wrote. "I still have a ton of work to do on myself, with my addiction, and clearing the wreckage of my past."