John Hileman, a Houston-based assistant U.S. attorney, has reportedly left a case involving memebers of the Aryan Brotherhood of Texas, citing "security concerns," the Huffington Post reported.

"He sent the email to every lawyer representing a defendant in the Aryan Brotherhood federal case, and he said -very short email - that he was withdrawing for security reasons," Houston defense attorney Katherine Scardino told Talking Points Memo.

The Associated Press has reported that authorities are investigating whether white supremicists were the main culprits behind a recent bout of violence perpetrated against prosecutors, in which DA Attorney Mike McLelland, who was killed with his wife, along with Assistant DA Mark Hasse, and  Colorado's Department of Corrections Tom Clements.

Texas law enforcement agencies have been put on high alert, the AP reported.

Scott Burns, executive director of the National District Attorneys Association indicated Tuesday that the slaying of prosecutors in the U.S. is "beyond rare," but that there no need for overreacting for the recent shooting, CNN reported.

Burns said the best available figures show that only 13 prosecutors have been killed in the line of duty over the past 100 years.

The National District Attorneys Association has also issued a statement to "remind all prosecutors to continue to be vigilant with respect to their personal safety and take appropriate steps should they receive any threats or cause for concern."

The Justice Department also took a low key approach.

"We always take the safety of Justice Department personnel extremely seriously and take appropriate steps when warranted," said Justice spokesman Wyn Hornbuckle.