YOLO COUNTY --
Just after midnight Saturday, 23-year-old Samantha Green was arrested on a murder charge, in the death of her three week old baby, Justice Rees.
"We have come to the conclusion that ms Samantha green was the sole individual responsible for the death of her child," said Yolo County Sheriff, Ed Prieto.
The arrest comes almost three days of around the clock investigating.
It's a case that has gripped the community, even police were emotionally invested.
"This is probably one of the top five worst situations I've ever been involved in or seen and this investigation is not over its gonna continue," said Sheriff Prieto.
As investigators search for a motive, here's what we do know:
Monday Green and baby Justice were reported missing.
Tuesday evening, search crews found mom dehydrated, cold and hysterical, in a slough in Knights Landing.
Wednesday morning a pain-staking search for baby Justice ended when he was found dead.
The possible cause of death: hypothermia and drowning.
FOX40's request to interview Green from jail was denied.
One neighbor tells us he heard the young mom was not doing well.
"Just that she was a really troubled person and that she was having a hard time caring for her baby and they were looking, trying to adopt it," said neighbor, Dave Petsick.
After she was found, Green claimed she was abducted and sexually assaulted.
Investigators say that story had no validity.
The Yolo County Sheriff says his team of detectives worked slowly and methodically before making the arrest.
"There's a lot of issues.. a lot of reasons why the detectives finally reached the conclusion that they did. It came through good investigative procedures and abilities...The individuals we spoke to - not only with Samantha green but anyone else that was connected," said Sheriff Prieto.
Now the case is in the hands of the Yolo County District Attorney's office.
Green has no criminal record.
Her first court date will be early next week.