When First Brands, an auto-parts maker, filed for bankruptcy late last month, it was not the sort of event that would typically draw attention in the world’s financial capitals.

A midsize manufacturer of pumps, filters and other under-the-hood products sold at retailers like AutoZone and Walmart, the company had expanded in recent years and had, it would appear, simply grown too quickly.

But now, the company is at the center of swirling milieu on Wall Street and beyond over the loans that fueled its rise and the questionable accounting, some of its creditors say, that preceded the fall.

Some well-known firms in international finance have been swept up in the fallout from company’s collapse, in some combination of losses, finger-pointing and embarrassment at having missed the signs of danger. That group includes Jefferies, the New York investment bank that arranged much of First Brands’ financing; UBS, the Swiss bank that provided a big chunk of the money; and BlackRock, which funneled money to an intermediary that lent it to the company.

The total losses are expected to tally into the billions of dollars, according to Texas bankruptcy court filings and people involved in the negotiations over what comes next.

This week, a representative of one of the company’s creditors said in a court filing that as much as $2.3 billion of assets had “simply vanished.”

But it is not solely the sum of the potential losses that has so many financiers on edge. Many of the loans to First Brands originated from the booming, loosely regulated world of “private credit.”

Unlike traditional banks, private credit lenders say, they have the ability to lend quickly because they understand complicated, risky businesses and do not need to worry about repaying ordinary depositors or reporting public earnings.

Trillions of dollars have been plowed into private credit over the past decade, principally from pension funds, endowments and other groups that rely on such investments to fulfill obligations to retirees and the like.

The Trump administration made moves this summer to allow 401(k) plans to invest savings into the private equity funds that extend private credit to companies, raising the stakes even further.

The First Brands bankruptcy could amount to something of an I-told-you-so moment for the traditional bankers and private-credit skeptics who have long maintained that these upstart lenders deserve more scrutiny.

Before its unraveling, First Brands was seen as a success story. Founded by Patrick James, a Malaysian-born businessman, the Cleveland company expanded rapidly over the past decade by buying 15 competitors, including brands such as FRAM (air and oil filters) and Autolite (spark plugs).

First Brands sells most of its products directly to the public on five continents and the rest to carmakers, which sell them under their own names. It says that it employs 26,000 people and that its sales totaled $5 billion last year.

A First Brands spokesman wouldn’t name the cars that include its components, but one hint in its bankruptcy filing is that the credit arms of Ford Motor and General Motors are among the companies it owes money. A General Motors spokeswoman said the company was monitoring the situation but did not anticipate any “material interruption to our operations.”

To pay for its acquisitions and inventory, First Brands borrowed heavily. It did so both in the open and in harder-to-trace ways, filings show, or both “on” and “off” its balance sheet of financial accounting.

On First Brands’ balance sheet was $6 billion of junk-rated debt, or loans the company took out at high interest rates in traditional fashion. This is neither unusual nor noteworthy on Wall Street. Nor did it raise many immediate concerns when the company this summer hired Jefferies, the investment bank, to help it renegotiate the debt’s terms for more time to pay back the loans.

During that process, however, First Brands’ lenders began asking for more information on the company’s finances — and discovered that the auto-parts maker had a few billion dollars in “off balance sheet” debt.

The lenders now say in court filings that those hadn’t been fully disclosed and involved a complicated loop of legal entities and overlapping promises of repayment to various private-credit firms, including several part-owned by Jefferies itself.

Already, creditors say, they have uncovered trouble with First Brands’ use of invoices to borrow money. In this form of financing, which is not uncommon, lenders provide money that is meant to be repaid when specific retailers send in checks for First Brand products.

The idea is that this is a short-term, relatively low-risk arrangement so long as the retailer pays the invoice in a timely fashion.

The problem was that First Brands had pledged money from the same invoices to multiple lenders, essentially double or triple counting what it expected its customers to be paying, according to the bankruptcy filings.

Because these arrangements were held off the company’s balance sheet, creditors say they were not aware that the same invoices were pledged more than once.

Last month, with questions mounting, First Brands’ efforts to refinance its debt fell apart, and the company filed for bankruptcy not long after. The company said that it had less than $30 million left in its coffers and that there was nothing left in the accounts that were supposed to hold the collateral for the off balance sheet loans.

“There’s just a lot that we don’t know, to put it bluntly,” a lawyer for some of the firm’s creditors told the bankruptcy court this month. The same lawyer called First Brands’ financial structure a “black box.”

The interest in the company’s issues, which were earlier reported by The Financial Times, has been intense. During the first bankruptcy hearing, held remotely from Houston, the judge said there were 500 people listening in and asked that callers combine into single lines so that the court’s software could fit them all in.

During that hearing, a lawyer for the company and Mr. James blamed, among other factors, President Trump’s tariffs for First Brands’ woes, saying they “caused additional landing costs for goods.”

The lawyer said her clients generally denied any wrongdoing and attributed the company’s demise to “macroeconomic factors and headwinds that were outside of management’s control.”

Dozens of private credit lenders and hedge funds say they are out money. Private funds run by UBS say they are owed more than $500 million. BlackRock is also owed a sum that it hasn’t yet specified. Other lesser-known investors in private credit such as CarVal and Ellington Management Group are also in the queue.

Hardest hit for now is Jefferies. One of its asset management subsidiaries, Point Bonita Capital, had lent $715 million to First Brands to supply inventory to retailers like Walmart and Advance Auto Parts. The bank said in a statement that it hadn’t been paid for those loans since Sept. 15, and First Brands’ representatives have told the bankruptcy court that they are investigating whether that money was already sent to a different lender to satisfy another loan.

Jefferies’ stock has dropped 17 percent this week. A spokesman, Joseph Ziemer, said the bank’s potential exposure had been “dramatically overstated by many.”

Questions now turn to whether other auto-parts companies may also face troubles.

First Brands’ trouble “leads me to believe there are other suppliers that may also be at risk,” Erin Keating, executive analyst at Cox Automotive, said Friday.

Jack Ewing contributed reporting.