Federal officials moved Thursday to shut down a third bus company as part of the widening investigation of the Aug. 8 fatal bus crash in Sherman.

The bus from that crash, which left 17 people dead and was one of the worst in Texas history, was registered to a company that was being operated illegally by owner Angel De La Torre of Houston. Immediately after the crash, federal officials shut down that company and a second firm owned by Mr. De La Torre.

On Thursday, the Federal Motor Carrier Safety Administration expanded the ban to include a small San Antonio bus company. Investigators say Liberty Charters and Tours is unsafe because it uses buses owned by Mr. De La Torre.

"Liberty Charters leases and operates buses owned and maintained by Angel Tours, Angel De La Torre and/or Iguala BusMex," the order states.

"Liberty Charters' use of passenger vehicles which are subject to the egregiously deficient maintenance procedures of ... Angel De La Torre places its drivers and the motoring public at continued and substantially increased risk of serious injury or death."

The action also prohibits Liberty Charters from operating buses that have no connection to Mr. De La Torre.

On Thursday, a glum-sounding Jose T. Hidalgo, the firm's owner, declined to discuss how the government's action would affect Liberty Charters. Federal records indicate that the company operates just two buses and employs three drivers.

FMCSA Administrator John H. Hill said Thursday that the order was not based on Liberty's safety record, which is far better than that of Angel Tours, the De La Torre-owned firm that the government shut down June 23 after a long string of safety violations.

But Liberty, too, has been cited for safety violations multiple times this year. Federal records show that inspectors checked Liberty buses four times this year and reported problems ranging from out-of-adjustment brakes to absent drivers' service logs. On May 30, officials cited one bus for having bad brakes, a bad oil leak, an exhaust leak under the driver's carriage and no safety-glass exit window.

Mr. Hill said the relationship between Mr. De La Torre and Liberty Tours came to light as investigators from the U.S. Department of Transportation pored over records seized from Mr. De La Torre's office.

"Mr. De La Torre has been reluctant to speak to us," Mr. Hill said. "Every time we've approached, he has told us that his lawyers have told him not to speak.

"But through an administrative subpoena, we have been able to review many of his records, and we've been looking to determine whether he has any relationships with other carriers."

Calls by reporters to Mr. De La Torre's lawyer have not been returned.

Mr. Hill said investigators have found that companies in South Texas appear to often operate under different names but frequently share or lease buses with each other.

So far, his agency has moved to shut down only one company – Liberty – that has used Mr. De La Torre's buses, plus his own two companies. But Mr. Hill said others could follow, depending on what the investigation uncovers.

Three buses with Vietnamese Catholics left Houston the night of Aug. 7, including the one that crashed in Sherman shortly after midnight. The passengers were headed to a religious festival in Carthage, Mo. One of those buses was operated by Liberty and operated by a driver who has worked for Mr. De La Torre in the past.

Mr. Hill said any company that is found to use buses that Mr. De La Torre has owned or operated – or uses drivers recently on his payroll – will be shut down.

Meanwhile, the National Transportation Safety Board continues to investigate the cause of the Aug. 8 crash. A preliminary report is expected soon, but a full evaluation of the incident will probably take more than a year, officials have said.

Plaintiffs' attorneys have said lawsuits associated with the crash could seek more than $50 million, though recovering such sums may prove to be difficult, depending on whether an insurance policy will cover the crash.

On Thursday, a relative of three victims filed suit against the manufacturer of the bus, its driver and Mr. De La Torre, seeking at least $100,000 in damages.

The driver, Barrett W. Brossard, remains in critical condition and has not yet been able to speak to investigators.