NEW YORK » Several witnesses in a securities fraud case against pharmaceutical executive Martin Shkreli are concerned he will retaliate if they testify against him, U.S. prosecutors say in a court filing.

Federal prosecutors in New York are asking a judge delay a civil lawsuit that the U.S. Securities and Exchange Commission brought against Shkreli until after his criminal case plays out. They fear that if Shkreli is allowed to take depositions in the civil case, he will have access to information that isn’t normally disclosed until the late stages of a criminal case.

“Here, there is evidence that defendant Shkreli has taken steps to intimidate or threaten individuals in the past,” prosecutors wrote in filings Thursday.

Several of the witnesses told prosecutors they were worried Shkreli would retaliate against them if they testified because they “have been threatened” by Shkreli over past disputes, prosecutors said. One of the witnesses, who wasn’t identified in court papers, also told prosecutors that Shkreli reached out to them after he learned he was under investigation and “suggested that the witness agree to a false version of certain events,” authorities said.

Shkreli’s attorney, Benjamin Brafman, said the allegations against his client are “preposterous.”

“While his ‘keen intellect’ can at times be intimidating to mere mortals, nothing else about Martin Shkreli is intimidating at all,” he said.

Shkreli, 32, gained notoriety last year after a drug company he founded, Turing Pharmaceuticals, spent $55 million for the U.S. rights to sell a life-saving medicine called Daraprim and promptly raised the price from $13.50 to $750 per pill.

The former hedge fund manager was arrested in December after prosecutors said he lost investors’ money through bad trades and then looted Retrophin, another pharmaceutical company where he was CEO, for $11 million to pay back his disgruntled clients. Shkreli has pleaded not guilty to securities fraud and conspiracy charges.