But, according to local law enforcement, the bag did not contain trash.
Inside the bag was the newborn son which the woman, later identified as Alexis Avila, had given birth to just hours before.
Miraculously, the baby was discovered alive six hours later and is now in a stable condition.
Ms Avila, 18, was arrested and charged with attempted murder and felony child abuse in a case which has sent shockwaves across America.
Here’s everything we know so far:
Chilling 911 call as three passersby find ‘freezing’ baby in dumpster
The case unfolded on 7 January when police received a panicked 911 call at around 7:45pm on Friday from someone calling to say they had just found a baby in a dumpster
“We just found a baby in the god***n trash,” the male caller says, in the audio obtained by KQRE.
“He’s whimpering, he was not crying actually. I was looking for some stuff in the dumpster and we heard…
“We heard something I didn’t know it was a baby. Thought it was a cat.”
A woman’s voice is then heard joining the call, saying the infant was “very weak”.
“He’s still got his umbilical cord attached and he’s freezing cold, and he’s barely like… He’s very, very, very weak,” she says.
A faint whimpering noise from the baby is heard in the background of the phone call.
Hobbs Acting Police Chief August Fons said in a press conference on Monday afternoon that three people – Michael Green, Hector Jesso and April Meadow – had been going through the dumpster at the Broadmoor Shopping Center on the 1400 block of N. Thorps “looking for anything of value”.
Chief Fons said the trio heard what sounded like a baby crying and pulled out a trash bag, assuming they would find a dog or kitten inside, he said.
Instead, they discovered the newborn baby “wrapped in a bathtowel which was dirty and wet and had dried blood on it, with the umbilical cord still attached,” he said.
Surveillance footage from a nearby store shows the three people standing by a truck and looking through the dumpster before one of them pulls out a black trash bag and opens it.
One of the other people is seen quickly opening the bag as they realise its contents.
The woman pulls out the baby and cradles him, getting inside the truck in an attempt to keep him warm.
Meanwhile, one of the other people is seen on the phone.
Multiple flashing emergency responder vehicles are seen arriving on the scene minutes later.
Chief Fons said the baby was treated at the scene and rushed to hospital for treatment, where he was in a stable condition as of Monday.
The police chief praised the “quick response” of the three rescuers who were “pivotal” in saving the baby’s life.
Surveillance footage leads police to the young mother
Investigators tracked down the alleged culprit thanks to surveillance footage captured on the nearby store Rig Outfitters and Home Store, owned by Joe Imbriale.
The video, which has gone viral, shows a white car pulling up next to the dumpster at around 2pm on Friday afternoon.
The woman, later identified as Ms Avila, is seen stepping out of the drivers’ seat, opening the back door and taking a black trash bag from the backseat.
She then hurls the package into the dumpster before getting back into the vehicle and driving away from the scene.
The footage reveals that the baby had been in the dumpster in plunging temperatures of around 30 degrees Fahrenheit for around six hours.
Investigators were able to get a partial licence plate from the footage, which led them to Ms Avila’s family home.
There, Ms Avila’s parents said it was their daughter who drove the vehicle.
Surveillance footage shows mother tossing newborn in dumpster
When officers told the parents about the nature of their inquiry, they agreed to take Ms Avila to the police station, Chief Fons said.
Teenage mother says she ‘panicked’ because she didn’t know she was pregnant
Ms Avila allegedly confessed to investigators that she had given birth to the baby and tossed him in a dumpster hours later.
The teenager told officers she “panicked” after giving birth on Friday, just one day after finding out she was pregnant, said Chief Fons.
She said she sought medical attention on 6 January because she was suffering from abdominal pain and constipation.
It was only then that she was told that she was pregnant, said the police chief.
He said the teenager said she then began experiencing more stomach pains the following day and gave birth in a bathroom at her parents’ home.
She said she “panicked and did not know what to do or who to call” so she cut the umbilical cord, wrapped her baby in the dirty towel and put him in a trash bag, he said.
Ms Avila told investigators she then drove around for a while before deciding to put the baby in a dumpster, he said.
When asked what she thought would happen to her baby after she left him in the dumpster, the police chief said she “remained silent and could not answer”.
Ms Avila told investigators the identity of the baby’s father but Chief Fons said it is not being publicly released as he is a minor.
The young couple had split up back in August, according to the criminal complaint.
Ms Avila’s mother told investigators she had no knowledge of her daughter’s pregnancy.
However, some school friends cast doubt on Ms Avila’s claims she didn’t know she was pregnant, telling DailyMail.com she was “open about her pregnancy” in the fall before she stopped coming to school in December.
What’s next for mother and baby?
Ms Avila was arrested and charged with attempted murder and felony child abuse on 8 January.
The 18-year-old was released on bond less than two hours later after posting a $10,000 unsecured bond.
She is scheduled to appear for a hearing in Lea County District Court on Wednesday.
If convicted, she faces up to 15 years in prison.
Ms Avila’s baby son is now in a stable condition and is in the custody of New Mexico Children, Youth & Families Department (CYFD).
Teen mother says she was ‘unaware’ of her pregnancy before throwing baby into dumpster
It is unclear who will have custody of the baby in the long term, however he baby’s paternal grandfather said his family is now seeking custody of the little boy, who they have decided to name Saul.
Oscar Astorga told DailyMail.com that his 16-year-old son Stephen is the baby’s father and had thought his ex-girlfriend had suffered a miscarriage after they split up in August.
“Of course we’re trying to get custody. Of course. He is my grandson,” said Mr Astorga.
“That’s why we can’t comment on anything because we’re trying to get my grandson.”
Chief Fons urged parents in need to reach out for help.
“If you are struggling with a new infant, the best response is to find somebody who can help you with that,” he said.
“Contact us, and let us help you through the situation.”
All 50 US have “safe haven” laws enabling mothers in crisis to safely leave their newborn babies to designated people such as hospital staff without the risk of criminalisation.
In New Mexico, the law allows a parent to hand over their child safely within 90 days of their birth.