Philadelphia mother who fought for justice showcased in new docuseries 'Mother Undercover'

A gripping new docuseries from ABC News Studios debuts Thursday on Hulu as part of their summer true crime series.

It's called "Mother Undercover," and it documents the incredible lengths four mothers went to for their children.

One episode features a Philadelphia mother who did not stop until she got justice for her son.

Lisa Espinosa's son, Raymond Pantoja, was shot and killed by a drug dealer in North Philadelphia in April 2016.

When police weren't making headway, Espinosa took matters into her own hands, never giving up until the gunman was behind bars.

"I couldn't just sit around," Espinosa says. "I didn't want my son to be one of those in that 47% of unsolved cases. I got involved. I knew that the streets spoke. I knew that hitting the streets hard would allow me to get information and as many tips as possible to get to the detectives. My goal was to find my son's murderer."

Espinosa chased down leads and followed them across the city.

She says, at times, she was fearful. But the fight for justice, and her love for her son, fueled her unrelenting search.

Espinosa prevailed. She hopes this docuseries achieves two goals.

"One is to bring gun violence awareness because we have a national epidemic," Espinosa says. "Two is to bring hope and inspiration to families of unsolved cases. I want them to know that they do have the strength to make a difference, even in your darkest times."

Pantoja's killer remains behind bars.

"Mother Undercover" is streaming now on Hulu.

The Walt Disney Company is the parent company of Hulu and this ABC station.