The US Department of Justice (DOJ) has begun a criminal investigation into Blue Bell Creameries’ Listeria monocytogenes outbreak last April.

Three people were killed and ten fell sick after they consumed the company’s ice creams, which were contaminated with Listeria bacteria, which can survive and grow in freezers.

The outbreak forced the Texas-based company to recall its products, including frozen yogurt and sherbet, and shut down three of its plants at Oklahoma, Alabama and Texas in April 2015.

"They knew that listeria was in their plant. It was a problem ongoing, longstanding, and they didn’t do anything about it."

Reports issued by the Food and Drug Administration (FDA) in early May showed evidence of unsanitary conditions at Blue Bell’s production facilities.

According to the FDA, the bacteria contamination was reported to the Blue Bell officials as early as 2013, along with other in-plant sanitation problems.

Food safety lawyer Bill Marler was quoted by NBC News as saying: "Their inspection reports and what the FDA found when they went there in the spring were pretty horrific.

"They knew that listeria was in their plant. It was a problem ongoing, longstanding, and they didn’t do anything about it."

Led by Patrick Hearn, the Department of Justice’s (DOJ) consumer protection branch has been entrusted with the responsibility to investigate whether the executives knew about the reports, and if so, why the reports were ignored.

Stores at many southern states, including Texas and Alabama, have been restocked with Blue Bell products after the company successfully reopened its factories over the last few months.

The company has assured consumers that its products are now safe to be consumed.