(Reuters) - A federal judge in Houston has thrown out a lawsuit accusing UBS Group AG of hiding fraud by its client Enron Corp from retail customers, a decision that may end a 15-year legal battle stemming from the energy company’s December 2001 bankruptcy.

The logo of Swiss bank UBS is seen at a branch office in Zurich, Switzerland January 27, 2017. REUTERS/Arnd Wiegmann

In a 228-page decision on Tuesday, U.S. District Judge Melinda Harmon said UBS PaineWebber brokerage customers failed to show that the Swiss bank intended to defraud them into buying Enron securities.

The customers accused UBS of trying to generate more fees by taking part in five transactions with Enron, such as loans and note offerings, that had no legitimate business purpose and that were designed to create a facade that Enron was healthy.

But the judge said: “It was Enron (and its accountants and lawyers) ... that was responsible for using these transactions to ‘cook its books,’ creating its allegedly fraudulent financial statements,” and ultimately defrauding the investing public.

The plaintiffs failed to specify “exactly what nonpublic, material information the UBS entities knew about Enron, who discovered it, when, how, and under what circumstances and why it was fraudulent,” Harmon wrote.

Lawyers for the plaintiffs did not immediately respond on Wednesday to requests for comment.

The plaintiffs chose to sue independently of other Enron investors who pursued similar claims in nationwide litigation.

A $7.2 billion securities class-action settlement in 2006 with several banks and other defendants over Enron’s collapse remains the largest on record.

Harmon had dismissed claims against UBS by another group of Enron investors on Aug. 2. Tuesday’s decision ends all Enron-related litigation for UBS, pending any appeals.

“UBS is gratified by the court’s dismissal of this case,” spokeswoman Erica Chase said.

Once ranked seventh on the Fortune 500 list of large U.S. companies, Enron went bankrupt on Dec. 2, 2001.

Its demise led to reforms including the federal Sarbanes-Oxley Act of 2002 and was the basis for the Oscar-nominated 2005 documentary “Enron: The Smartest Guys in the Room.”

Several executives went to prison, including former Enron Chief Executive Officer Jeffrey Skilling for fraud and other offenses.

He is eligible for release in February 2019, federal prison records show, after having his sentence shortened to 14 years from 24 years in 2013.

Kenneth Lay, Skilling’s predecessor and successor as CEO, was also convicted of fraud but died in 2006 before he could be sentenced.

The case is Lampkin et al v UBS PaineWebber Inc et al, U.S. District Court, Southern District of Texas, No. 02-00851.