YOLO COUNTY (CBS13) — Yolo County Sheriff Ed Prieto formally announced the arrest of Samantha Green during a press conference on Saturday.

Prieto said Green, 23, was arrested at 12:15 a.m. on Saturday, for the death of her son, 20-day-old Justice Rees.

Investigators previously indicated Green and Justice were the only ones in the car, and that she was likely not the victim of an attack. Prieto reaffirmed that on Saturday.

“There is no other additional evidence indicating someone else is involved, at this point,” Prieto said.

Green and Rees went missing on Feb. 21 when they didn’t arrive at a family event. A frantic search ensued, and on Tuesday night, Green emerged from a Knights Landing slough on Tuesday night, telling a man who lived nearby to call 911 and that her baby was dead.

Search crews worked through the night on Tuesday to find Justice, but it wasn’t until Wednesday morning that they found the baby’s body.

The Yolo County coroner said on Thursday that while an official cause of death for Baby Justice would still be weeks away, drowning and hypothermia were two possibilities. Justice’s grandmother told CBS13 she was relieved the autopsy did not reveal obvious signs of trauma or injury to the baby.

Detectives indicated Green was much more responsive during a questioning session late Friday night before her arrest.

Prieto would not comment on the state of Green when she was discovered or during questioning. When asked about her mental state, or if she was depressed, the sheriff said that is an issue for experts beyond the sheriff’s department to tackle.

“Before she seemed—I don’t want to use the term hesitant or evasive. She just wasn’t sure. But I think that probably had more to do with her physical condition,” Prieto said, saying she was dehydrated.

Green will face a murder charge, but it’s up to the Yolo County District Attorney ‘s Office to determine which one, Prieto said.

The investigation has been hard on the community and his deputies, Prieto said.

“This is probably one of the Top 5 worst situations I’ve personally been involved with or seen,” he said. “It touched our souls. We wanted to make sure we were really slow and methodical in coming to this determination.”

Prieto also sympathized with Green’s family as they process the death of Baby Justice, and the arrest of his mother.

“I can only imagine what her family is going through,” Prieto said.

LIVE: Sheriff: No motive at this point in #BabyJustice murder. DA will determine murder charge http://t.co/CQUu1oDBJa — CBS Sacramento (@CBSSacramento) February 28, 2015

LIVE: Toxicology results for baby and mother may take 3-4 weeks. #BabyJustice http://t.co/QScfxFhH88 — kylebuis (@kylebuis) February 28, 2015

Sheriff: Whether Green suffered from depression is way beyond investigators, that's for experts http://t.co/QScfxFhH88 — kylebuis (@kylebuis) February 28, 2015

Did Samantha Green confess? Sheriff Prieto: "Any comments between her and the detectives are confidential." #BabyJustice — Adrienne Moore (@AdrienneMooreTV) February 28, 2015

Sheriff: "I can only imagine what her family is going through." http://t.co/QScfxFhH88 — kylebuis (@kylebuis) February 28, 2015

Sheriff: Search started as a rescue operation http://t.co/QScfxFhH88 — kylebuis (@kylebuis) February 28, 2015

Sheriff: "I'm extraordinarily proud" of the work deputies and investigators have done on case #BabyJustice http://t.co/QScfxFhH88 — kylebuis (@kylebuis) February 28, 2015

Yolo County Sheriff Ed Prieto: "This is one of the top five worst situations I've ever seen." #BabyJustice — Adrienne Moore (@AdrienneMooreTV) February 28, 2015

Sheriff: "You're innocent until proven guilty; I'm a strong believer in that." #BabyJustice http://t.co/QScfxFhH88 — kylebuis (@kylebuis) February 28, 2015

For more on this story, visit our Baby Justice page.