The owners of 'The Clyde', the Oak Cliff apartment complex destroyed in a May explosion that killed three people, are suing Atmos Energy Corp.

The lawsuit alleges "the explosion was caused when Atmos failed to properly mark its gas pipeline, which Atmos has known since at least 2004 was susceptible to brittle cracking and catastrophic failure."

The lawsuit also alleges Atmos was notified about the planned drilling at the complex and "failed to shut off the gas after being notified of an active gas leak" on the day of the explosion.

The owners claim the failure to accurately mark things underground "directly caused the drilling company to strike the unmarked line."

NBC 5 emailed Atmos Energy on Friday morning to ask for a response to the lawsuit.

The company responded with a statement that reads in part:

"Atmos Energy is actively supporting investigations by the National Transportation Safety Board (NTSB), the Railroad Commission of Texas, emergency responders, and all parties involved as they work to determine the cause of the incident. The NTSB issued a preliminary report on July 1, which is available here."

In the statement, Atmos Energy said it hired a contractor to locate and mark the lines, which is reflected in the NTSB report. Those preliminary NTSB findings say some gas lines had been marked; however, the gas line struck on May 28 had not been marked.

A separate lawsuit filed in early July on behalf of the victims' family also focused on whether the gas lines were properly marked.

A second lawsuit has been filed against Atmos Energy following the deadly apartment explosion in Oak Cliff that claimed three lives. The lawsuit alleges the utility company bears responsibility in connection with the explosion. NBC 5's Maria Guerrero breaks down what it could mean as the investigation continues.

Last month, a judge ordered Atmos to preserve evidence from the explosion.

Atmos' statement concludes with:

"The most common cause of outside natural gas leaks is digging or construction that disturbs natural gas pipelines. If you nick, scrape, or dent a natural gas pipeline, call 911 and then call Atmos Energy’s 24-hour emergency number at 866-322-8667. Even minor damage can weaken a pipeline and lead to a future leak."

For more information about digging safely, visit their website, and if you smell gas, evacuate the area, then call 911.

Atmos' resources for gas leaks:

• 24-hour toll-free emergency number at 866.322.8667
• atmosenergy.com/safety/home-safety

More than a month after the explosion at the Bonnie Apartments in Oak Cliff, residents are still living without natural gas service. A local nonprofit says it has encountered obstacles while trying to help those affected.