A Salt Lake City woman was charged Friday with trying to obtain a deadly and illegal biological agent to hurt her sick roommate.

Investigators with the Utah Department of Public Safety, the FBI and the U.S. Postal Service started looking into the woman after receiving a tip that she was trying to purchase the biological agent, an antibiotic-resistant strain of Staphylococcus bacteria that can cause skin infections and lead to pneumonia, sepsis and death, according to charging documents.

Law enforcement allege Janie Ridd, 50, meant to use the bacteria to harm or kill her roommate — and that this wasn’t the first time she’d tried. Charging documents note Ridd was the beneficiary of her roommate’s life insurance payout, and her roommate’s will designated that Ridd would take custody the roommate’s child.

Charging documents note that Ridd is the roommate’s legal caretaker, although their relationship recently had become fraught due to “power issues and control-type domestic violence dynamics.”

Court documents don’t list an attorney for Ridd, so The Salt Lake Tribune was unable to request comment.

Ridd allegedly began searching the dark web — a section of the web not accessible by conventional means — for the antibiotic-resistant bacteria in October 2019.

According to charging documents, Ridd found a vendor and told them she was a teacher and needed the bacteria for a science experiment at school. When the vendor told her that, as a teacher, she could purchase the bacteria from a legitimate source, she wasn’t dissuaded and offered to pay for overnight shipping so she could get the bacteria faster.

Charging documents note Ridd is not a teacher.

She paid $300-worth of bitcoin, an online cryptocurrency, for the bacteria and had it sent to a Salt Lake City address, the charges allege.

On Dec. 18, agents saw Ridd pick up her package. However, it wasn’t what she had allegedly ordered.

Agents had filled it with coffee containers and placed petri dishes containing fake Staphylococcus bacteria among the grounds.

Ridd took the package to her work, where agents confronted and interviewed her.

At first, Ridd told them the package contained expensive coffee she’d ordered online, but soon after she said it was actually a “biological” she’d purchased to make beer, according to charging documents.

Later, she said the package contained “staph" bacteria, which she wanted for “experimental purposes and to satisfy a personal curiosity she had stemming from her roommate’s recent exposure" to another Staphylococcus strain.

Police arrested Ridd at the end of that interview.

When investigators interviewed Ridd’s roommate — referred to as the “intended victim” in charging documents — the roommate outlined several strange incidents prior to Ridd’s arrest.

First, the roommate said that after a neck surgery in March 2019, a “suspicious" staph infection was found on the wound.

The roommate also recalled that after watching a true-crime television show with Ridd, Ridd stated that “she thought the best way to kill someone and get away with it would be to inject the victim with insulin.”

In June, the roommate, who isn’t diabetic, was hospitalized twice for dangerous blood sugar levels, court documents said.

Authorities say that Ridd purchased insulin on a certain marketplace on the dark web in September, and added that agents don’t know what other sites Ridd allegedly may have visited.

Then, in October, after the roommate and Ridd got into a fight over the roommate’s living will and custody issues regarding the roommate’s son, the roommate had another surgery.

“And, shortly thereafter, [the roommate] inexplicably developed three different golf ball-sized infections on the wound,” charges state. Test showed it was E. coli, which the surgeon said didn’t occur as a result of the surgery.

Ridd was booked into Salt Lake County jail Wednesday. She was charged Friday in third-district court with aggravated abuse of a vulnerable adult, a second-degree felony, attempted aggravated abuse of a vulnerable adult, a third-degree felony and attempted possession of a biological agent, a second-degree felony.

She remained in jail Friday, and prosecutors requested that she be held without bail, arguing Ridd poses a threat to her roommate.