WEST (CBS 11 NEWS) – The ATF is under fire.

It’s among the lead agencies investigating the fire and explosion at the West Fertilizer Company plant that killed 15 people last month.

READ MORE: Resentencing Hearing For 'Tiger King' Joe Exotic Happens Today In Oklahoma

Agents from another organization looking into the blast accuse the ATF of interfering and delaying their investigation.

The U.S. Chemical Safety Board is required by federal statute to conduct investigations into chemical industrial accidents.

Now, the board is asking for the Senate’s help in doing its job after what it describes as the ATF’s intimidation and delay tactics. The Board hopes to prevent what happened in West from ever happening again. But the Board chairman, Rafael Moure-Eraso tells me his team has been blocked from doing its work by another federal agency, the ATF, which headed the primary criminal investigation into the blast. “It’s going to be harder, it’s going to be a lot harder, and it didn’t need to be that way, that’s the problem.”

Moure-Eraso sent this strongly worded letter to U.S. Senator Barbara Boxer, chairman of the Senate Environment & Public Works Committee which may hold hearings on the explosion.

Moure-Eraso says the ATF actually turned away two board members, Presidential appointees, from the scene.

In his letter, he called it “an unprecedented and harmful delay.”

Moure-Eraso says, “We are especially interested in this place because the size of destruction that happened in a community is unprecedented.”

READ MORE: Frisco Memorial Girls' And Boys' Basketball Teams No Longer The New Kids On The Block

In fact, Moure-Eraso claims the Chemical Safety Board wasn’t allowed to conduct its first interview with a plant employee until nearly three weeks after the blast. And he says even that was interrupted by more overreach on the part of ATF. “There were three armed guards who decended over him, and said you have to come with us, we still need to talk to you, and we never saw this person again until four hours later.”

During a news conference last week, the ATF and State Fire Marshal were asked if they would turn over their findings and evidence to the Chemical Safety Board.

Assistant state fire marshal Kelly Kistner said, “We will not at this time. This is an on-going criminal investigation, and that information will remain protected under the applicable laws.” When asked if he tried calling the ATF to try to resolve this, Moure-Eraso said, “We did try to get into contact with the director of the ATF, here in Washington, but unfortunately, we didn’t get an answer from them.”

So what does the ATF say about all this? The agency declined comment.

In a statement released shortly before 6:00 p.m. Wednesday, the State Fire Marshal said the criminal investigation takes priority over others, that it and the ATF did assist the chemical safety board’s investigation, and that it gave chairman Moure-Eraso a personal tour of the scene.

Also Check Out:

MORE NEWS: Loophole In Federal Surprise Medical Bill Ban Leaves Patients At Risk Of High, Unexpected Ambulance Bills