UNION CITY — The victim in this murder case had no name until after she was dead.

On the day she was born in 2009, her mother allegedly drowned her inside their Union City apartment, then left her body in a dumpster, stuck to a Costco receipt, bloodied pantyhose and random trash, for a man searching for recyclables to find.

Union City police took it upon themselves to adopt her and give her a name: Matea Esperanza, the second name meaning “hope.” She would have celebrated her 16th birthday in May had she lived.

Cold case detectives took on the case with a simple approach: find the baby’s mother, and you’ve found the most likely murder suspect. Thanks to genetic data, social media postings and a secret trip to Denver, investigators now believe they have done just that.On Wednesday, Alameda County prosecutors charged Angela Onduto, 46, with murdering her newborn daughter, Matea, on May 18, 2009. Onduto, who has also gone by Angela Anderson and Angela Onken, allegedly confessed to the killing with “no remorse” when detectives went to her Denver home to interview her last month.

Onduto was arrested in Denver on Wednesday, and remains jailed there on a fugitive hold, pending extradition to California, court records show.

Charging records describe how the case came to be filed, 16 years after a man made a grisly discovery in a Parkside Apartments’ dumpster. He’d been looking for cans and bottles to trade for five cents apiece, and believed he’d found a baby doll — until his shock wore off. When he called police, his expertise in local dumpsters proved valuable. He explained that particular garbage can got emptied daily, meaning the newborn had been dumped there within 24 hours.

Media reports at the time said police publicly emphasized the baby likely died of natural causes. One report by this news organization refers to her as a “stillborn,” while another says she likely died from a rare bacterial infection contracted from her mother’s uterus.

But police say an autopsy later revealed an official cause of death: drowning.

Police interviewed neighbors. Onduto — who went by Angela Anderson back then — answered her door. She said she had no idea who might be responsible, a story she’d allegedly repeat in more detailed fashion weeks later when police followed up with neighbors. During the second go-round, she said she hadn’t even known about the incident until police swarmed the parking lot that day, authorities said.

The case went cold, but even without leads, Union City police kept Matea’s memory alive. In 2017, the department’s union purchased her a headstone. Last May, on her would-be 16th birthday, the department made a Facebook post encouraging the public to reflect for a few moments on her memory.

What the May 18 post didn’t say was that detectives were closing in on Matea’s suspected killer, and just weeks away from finally making an arrest.

In 2021, a new detective had been assigned to the case. By then, the genealogy technique — famous for catching the Golden State Killer in 2018 — had been developed. It involves tracking down suspects’ potential relatives through public DNA databases, and detectives used it to narrow their suspect pool down to two, including Onduto.

When they reviewed Onduto’s history, they realized she’d lived at the apartments on Decoto Road where the newborn’s body was found. It turns out that Onduto had been connected to the case in another way as well — the Costco receipt stuck to Matea’s body was linked to her account, authorities said.

By the 2020s, she’d moved to Denver. Police planned a trip there, where they trailed her until they saw her discard a beverage cup in public, then collected it for testing, authorities said. Subsequent DNA tests — on the cup, Matea, and the bloody pantyhose found next to her body in the dumpster — all reportedly lined up.

Last month, police went out to Denver again to question Onduto about what had happened. A probable cause declaration, signed by Union City Detective Dominic Ayala, says what allegedly happened next.

“Angela detailed how she intentionally murdered (Matea) after giving birth at home in 2009. Angela expressed no remorse, and said she knew while pregnant she had no intention of keeping the baby,” Ayala wrote. “She admitted to discarding Baby Jane Doe in the dumpster. She denied diagnosis with any psychiatric conditions and/or drug use at the time of the incident.”

Matea’s remains are buried at Chapel of the Chimes in Hayward.