Chandler police and fire investigators were joined by the ATF agents and Southwest Gas officials as they tried to determine the cause and origin of Thursday's explosion.
The explosion inside a Platinum Printing, near Ray and Rural roads, seriously injured four people and forced evacuations.
ABC15 learned Southwest Gas crews detected a possible underground gas leak near the strip mall print shop. Some additional businesses and homes were evacuated, and gas to the area was shut off as utility crews worked to ensure the area was safe.
It's not clear if the possible leak happened prior to the explosion or afterward.
Workers dug ditches, brought in new pipes, and looking at gas connections to businesses behind the strip mall.
The ABC15 Investigators asked Southwest Gas and the Chandler Fire Department if anyone had reported smelling gas or a leak prior to the blast. ABC15 also asked if any utility work had recently occurred in the area. Neither agency provided answers.
"It wasn't the natural gas that we smelled," said Mark Schiele, who lives directly behind the printing business. "After the explosion, you could smell nasty chemicals in the air, and it wasn't like any regular fire smoke smell, which concerned us.
ABC15 also asked the Chandler Fire Department whether the print shop owners had previously reported to them what, if any, hazardous materials were inside the building. ABC15 is still waiting on that answer.
It's unclear where nearby businesses and homeowners should report damage and whether they'll get any help with repairs.
In a statement from the ATF Thursday, they say:
"The National Response Team (NRT) of the Bureau of Alcohol, Tobacco, Firearms and Explosives, along with ATF special agents from the Phoenix Field Division, were activated today to join the investigation of the explosion that occurred at a commercial printing business, located in Chandler, Arizona. This is the 875th NRT activation since it’s inception and 12th activation this year.
The NRT callout will have experts arriving Friday and they will begin processing the scene. ATF’s NRT was activated to join the investigation at the request of the City of Chandler. The NRT members will be working jointly with investigators from Chandler Fire and Police Department."
“ATF is committed to working alongside the Chandler Police and Fire Department to determine the origin and cause of this explosion that tragically injured four individuals ,” said Special Agent in Charge of ATF Phoenix Field Division Gabriel Pinon in a statement.