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WEST MEMPHIS, Ark. — An investigation into a private ambulance service based in West Memphis has involved officials at the federal level, according to officials with the Drug Enforcement Administration.

Related: Arkansas ambulance service can’t perform certain life-saving procedures

Medical director Dr. Michael Johnson resigned last week amid the investigation, led by the Arkansas Department of Health. As a result, Crittenden EMS lost its Advances Life Service privileges, known as “ALS.” ALS includes administering narcotics on ambulance trips.

WREG spoke with Johnson Thursday. He said he spends most of his time as an emergency room physician at an Arkansas hospital, keeping him away from work in EMS. That’s part of the resignation.

“They needed a director who can be more hands on, who could be on grounds more often,” he said.

But the bigger reason has to do with the Department of Health investigation regarding “potential regulatory violations,” he said.

“They were transporting some narcotics from West Memphis to the Wynne service. It was supposed to be in an ambulance with a lockbox and they transported it in a company truck,” he said of the reason for the investigation.

He did not know how the DOH found out about the potential violation.

He said he found out about the DOH investigation six weeks ago and resigned on October 2, leaving the company without a physician. According to a DEA spokesperson, the Arkansas DOH contacted them about Dr. Johnson’s involvement. Johnson voluntarily surrendered his paramedic DEA license, he said. The DEA spokesperson said the agency is not investigating Crittenden EMS as a whole.

“Anytime [the DEA gets] involved in anything, it makes me take note and be cautious about the way I handle things. To me, it was better to step down,” Johnson said.

When WREG spoke with Crittenden EMS’s owner Hudson Hallum Wednesday, he said he didn’t know there was a problem. He thought the DOH had just done a recent routine inspection.

“They have not notified us that there are any regulatory violations,” Hallum said.

“I don’t know what he said or meant by that. He’s known about it but not much about it,” Johnson said.

WREG also asked Johnson whether the public should know about this change.

“They don’t have the capabilities they had when they were a full ALS unit. Absolutely, the community should know,” he said.

WREG asked: “Do you think he would’ve come forward with that information if we hadn’t been covering it?”

“I would think not, I don’t know anybody would’ve done that,” Johnson said.

Hallum pleaded guilty to a federal conspiracy charge in 2012 after admitting to bribing voters.