This undated handout photo provided by the Dallas County Sheriff's Department shows Dr. Christopher Duntsch. Dallas County Sheriff's Department via AP A Texas neurosurgeon facing criminal charges alleging he may have intentionally hurt patients who had turned to him to resolve debilitating injuries sent a chilling email to his girlfriend saying he was ready to "become a cold blooded killer," according to prosecutors.

Authorities in Dallas County say Christopher Duntsch's hands and the surgical tools he used amounted to "deadly weapons" as he performed surgeries.

They contend that Duntsch "intentionally, knowingly and recklessly" harmed up to 15 patients who underwent spinal surgery from 2011 to 2013, when the Texas Medical Board revoked his medical license.

According to the Washington Post, his former colleagues at the Dallas Medical Center described him as a "sociopath."

Duntsch is accused of wide-ranging malpractice that includes improperly placing screws and plates along the spines of patients, leaving a sponge in one patient and cutting the major vein of another, according to a search warrant and records on file with the medical board.

He also operated on the wrong part of a patient's spine, damaged nerves and left one woman with chronic pain and dependent on a wheelchair, according to criminal and civil court records.

In one particularly horrifying instance, authorities allege Duntsch operated on his roommate and friend after a night of using cocaine. The man emerged from the operation a quadriplegic, according to the Washington Post.

Duntsch, 44, is charged with five counts of aggravated assault causing serious bodily injury and one of causing injury to an elderly person, all relating to four people who were severely injured and one woman who died in July 2012.

Authorities indicted Duntsch last month, but it was not until a recent bond hearing that prosecutors introduced an email they say was written by Duntsch to his girlfriend.

"I am ready to leave the love and kindness and goodness and patience that I mix with everything else that I am and become a cold blooded killer," he allegedly wrote in December 2011.

He remains jailed after a judge Friday declined to lower his $600,000 bond.

Duntsch defense attorney Robbie McClung said Tuesday that the email from 2011 was submitted without any context, arguing that the tone is not clear and he may have been using sarcasm. She said authorities have not proved a criminal case.

"I think everyone is reading an awful lot into an email," she said.

Police say in a search warrant affidavit that Duntsch is being investigated for surgeries done on at least 10 other patients, and allege he "knowingly takes actions that place the patients' lives at risk," The Dallas Morning News reported.

The medical board says his actions led to the death of a second patient, following an operation at a hospital in Collin County, just north of Dallas County.

McClung said authorities have not independently investigated allegations against Duntsch and have done nothing more than "rubber stamp" claims made in civil lawsuits.

"There's a great deal of indication that this is not anything but malpractice," she said.

Messina Madson, a top Dallas County prosecutor, through a spokeswoman declined Tuesday to provide further details or comment.