Cassandra Collins claims Arias threatened to get revenge against prosecutor Juan Martinez if she was given the death penalty, KSAZ-TV in Phoenix reported Tuesday.
"She said that if she was given the death sentence ... she wanted to get her revenge... . She knows inmates on the outs [outside] to do a mafia bow tie ... . Cut his throat," Collins said.
Arias also asked Collins, "Why doesn't Juan Martinez love me?"
Collins said she replied, "He's your prosecutor. He's there to prosecute you for a crime."
The former Arias cellmate said she decided to tell her story because she was worried about Martinez.
"He need to get good security staff around him to make sure she can't get anybody on the outs to solicit something, to harm him or to hurt him," Collins said. "She's very dangerous, very dangerous."
Arias was convicted in May of murdering ex-boyfriend Travis Alexander. The jury deadlocked on whether to give Arias the death penalty, and the judge declared a mistrial on that portion of the trial.