A Dulzura man pleaded guilty to trying to poison and kill his wife Tuesday by repeatedly feeding her a dangerous chemical once used in rat poison, according to the San Diego County District Attorney's office.

Race Remington Uto, 27, an active-duty Navy sailor, was arrested in March and faced three counts of attempted murder after a multi-agency investigation.

More than two weeks before Uto's arrest, his wife was admitted to an area hospital with an unknown illness, SDSO Lt. Greg Rylaarsdam said. Medical staff was able to determine that the woman had an "extreme level of Thallium in her system."

SDSO detectives believe Uto's wife had ingested the chemical in her food and drink over the span of months.

The DA said his actions were premeditated.

A navy man had allegedly been poisoning his wife for months in Dulzura without her knowing. NBC 7's Megan Tevrizian is outside the El Cajon courthouse with more information.

According to an affidavit, Uto's wife began feeling sick last September and eventually got so sick that she lost all of her hair and could barely move her limbs.

Thallium is a heavy metal that was used as a rat poison and ant killer until it was banned in the 1960s.

The chemical is so dangerous that it's considered a weapon of mass destruction by the U.S. government and can't be purchased over the counter anywhere in San Diego County.

Friends and family of Uto's wife created a GoFundMe page to help her as she recovers.

Uto will be sentenced on March 14, 2019, and could face 21 years to life, the DA's office said.