Shayanna Jenkins was granted immunity by the court in February, which means she can be compelled to testify or face time behind bars. There had been a question over whether prosecutors would call Jenkins, who has been in a relationship with Hernandez, 25, since high school and is the mother of his 2-year-old daughter.
The two people spoke to the AP on Thursday on condition of anonymity because of a gag order that's in place.
Jenkins, 25, has pleaded not guilty to perjury. Prosecutors say she lied to a grand jury investigating the June 17, 2013, killing of Odin Lloyd, who was dating her younger sister, Shaneah. Lloyd was found shot to death at an industrial park less than a mile from the home that Jenkins and Hernandez share.
Shayanna Jenkins has been coming to court sporadically and sitting behind Hernandez, whispering "I love you," to him at breaks and occasionally joking with him. She has not appeared in court since March 6. That day, she was not wearing a large diamond engagement ring that she usually sported on her ring finger.
Shaneah Jenkins, 23, testified for prosecutors earlier in the trial. When she appears in court, she sits with Lloyd's mother and other family members. During Shaneah's testimony, Shayanna scribbled notes and then passed them to Hernandez's lawyers at breaks and occasionally sighed as her sister spoke.
The day after the killing, Shaneah Jenkins testified, her sister asked to borrow her car to go get money for the house cleaners.
Shaneah testified she saw her sister carry a garbage bag to the basement. Surveillance video later played for the jury showed Shayanna then removing what appeared to be a box from the basement and putting it in the trunk of her sister's car.
Prosecutors said before the trial that they believe the box contained the gun Hernandez used to kill Lloyd. The murder weapon has never been found.
The sisters introduced Hernandez and Lloyd to each other in August 2012, when, for Shaneah's birthday, Hernandez got them a skybox for a Patriots game at Gillette Stadium.
Also Thursday, the trial was briefly disrupted by a bomb threat called in to the courthouse. No explosives were found, and employees were let back in about an hour later.
Superior Court Judge Susan Garsh told jurors after they returned that there was no reason to believe the interruption was related to the Hernandez case.
Earlier, the court released Garsh's decision that prosecutors may introduce into the trial jailhouse calls Hernandez made in which he discusses giving money to a cousin. Prosecutors say the promises of money were used to buy her silence after the killing.
Garsh said she would also allow a July 12, 2013, call in which Hernandez, speaking from jail, tells his cousin Tanya Singleton: "Obviously don't say nothing."
"I'm not saying nothing," she replies.
Singleton, who has terminal cancer, spent seven months in jail for refusing to testify before a grand jury investigating Lloyd's killing. She has also pleaded not guilty to helping Hernandez co-defendant Ernest Wallace flee to Georgia.
In a July 23, 2013, conversation from behind bars, Hernandez is recorded saying he set up trust funds of $75,000 or $100,000 for Singleton's two sons, which he says would double every seven years.
In fact, he never set up the trust funds.
Singleton's sister, Jennifer Mercado, completed her testimony in the case Thursday. Mercado, who was granted immunity and ordered by the court to testify, said on the stand this week that Wallace and Hernandez's other co-defendant, Carlos Ortiz, sometimes smoked PCP and that Wallace would act crazy, jittery and erratic.
She said surveillance video taken at Hernandez's home in the early morning hours before the killing showed the two men acting jittery. But upon seeing more video Thursday from that morning and later that day, Mercado said it did not appear that Wallace and Ortiz were acting erratic or crazy.
Wallace and Ortiz have pleaded not guilty and will be tried separately.
Associated Press writer Denise Lavoie contributed to this report from Boston.