The FBI is investigating allegations against a Texas abortionist whose former employees say he killed infants who survived abortions by "slashing or twisting their necks".

The Justice Department notified pro-life group, Operation Rescue, of the progress of the investigation in a letter dated May 11, 2018.

According to the letter, the investigation on abortionist Douglas Karpen is being forwarded to the FBI Houston field office for "any action deemed necessary" related to the murder of killing babies after failed abortions.

Operation Rescue first released a report about Karpen after four women who use to work with him at a Houston facility contacted the group claiming he violated the law. That report led to a grand jury investigation of Karpen.

"When he did an abortion, especially an over 20-week abortion, most of the time the fetus would come completely out before he cut the spinal cord or he introduced one of the instruments into the soft spot of the fetus, in order to kill the fetus," Deborah Edge said.

Edge worked as a surgical assistant for Karpen for nearly 15 years before resigning in March 2011.

"I thought, well, it's an abortion you know, that's what he does, but I wasn't aware that it was illegal. Most of the time we would see him where the fetus would come completely out and of course, the fetus would still be alive," she added.

The women also submitted graphic images taken on one of the employee's cell phones to Operation Rescue.

"They depicted two babies aborted well beyond the legal limit of 24 weeks in Texas. Their necks had been cut," the group reported at the time.

"The photos show babies that are huge, with gashes in their necks, indicating that these babies were likely born alive, then killed, just as Kermit Gosnell did at his 'House of Horrors' clinic in Philadelphia," Troy Newman, president of Operation Rescue, said in 2013.

Despite the evidence, the grand jury did not indict Karpen at that time.

Operation Rescue later learned that the grand jury had improper communication between then-District Attorney Devon Anderson and Karpen's criminal defense attorney Chip Lews, who were close family friends. Lewis also donated $25,000 to Anderson's political campaigns.

This, however, did not stop the group from taking further actions. The allegations against Karpen were forwarded to the U.S. House Select Panel on Infant Lives. In 2016, the panel referred Karpen to the Department of Justice under former Attorney General Loretta Lynch, but no action was taken.

Operation Rescue's Cheryl Sullenger continued to press for action and in 2017 she wrote a letter to Attorney General Jeff Session asking him to open an investigation into Karpen's actions.

The DOJ responded confirming that the issue is being reviewed.

"The letter I received from the Department of Justice is encouraging. The photos depict wounds inflicted on those babies that could not have been done inside the womb," Sullenger said.

"After having personally attended the Pennsylvania trial of Kermit Gosnell, who was convicted of murdering living babies after failed abortions, I knew we could never give up seeking prosecutions for Karpen's similar crimes," she continued. "We are grateful for this new FBI investigation that has renewed our hope that Karpen may finally be brought to justice."