The remains of 25-year-old Rachel Castillo were found Sunday in a remote location of the Antelope Valley.
She was reported missing after her sister found a bloody scene at her home on Thursday, Nov. 10.
The discovery triggered a search for Rachel, whose cellphone, car keys and vehicle were still at the home she shared with her sister Emily.
Detectives later arrested Rachel's ex-husband, Zarbab Ali, a 25-year-old Hawthorne resident. He was arrested at his parents' home in Victorville "in connection to Rachel's homicide."
Rachel's mother, Robyn Castillo, spoke with ABC News on Sunday and said she had spoken with Ali over the weekend in what she described as a "very normal" conversation.
"He had my grandchildren, I had texted him to ask how he was doing," she said. "He offered to video chat so I could see the boys. I got to see my grandsons and speak to them and he expressed his concern and I just told him we're doing everything we can ... he said he was very sorry and hoped that she was okay. It seemed like a very normal conversation."
Police say Rachel's children are safe. The mother said the couple's relationship was mostly amicable, though she added there were "some difficulties" along the way.
"I really didn't expect it to turn out like this," she said.
Meanwhile, Rachel's father, Christopher Castillo, said he and his friends, who are retired members of FBI, were working the case on their own, separately from police, while also sharing information.
"Here's a mom who divorced her husband, worked in a domestic violence prevention center and worked with battered moms ... and you know, it's kind of obvious why she probably divorced her husband," he said. "I mean the guy ended up showing up and murdering you."
Family members and friends held a vigil early Sunday evening to honor Rachel and seek the public's help for what was then considered a missing-person case.
It appears at the time they were not aware of the new developments in the case.
"I'd like to not draw on what happened to her and who harmed her," said Rachel's mom. "I really want to celebrate my daughter's life. She was a beautiful person. She was a wonderful mother, a wonderful daughter, sister, granddaughter, friend ... she was very important to so many people and she just she really just wanted to help people and be there for others, and I just want everybody to remember that, and lets not dwell on what happened to her and who harmed her. Let's celebrate her life."
Ali is currently being held at the Ventura County main jail on a $510,000 bond. He's expected to appear in court on Tuesday.
Police have not released additional details, saying "some details cannot be released due to legal and investigative reasons."