A Mexican activist searching for her daughter who disappeared early last year was shot dead Tuesday -- the latest murder of one of the relatives of the country's many missing persons.

Esmeralda Gallardo, a member of a group called The Voice of the Disappeared, was gunned down on her way to work in the central city of Puebla, prosecutors said.

She had been looking desperately for her daughter Betzabe Alvarado for more than a year.

The 22-year-old was last seen in January 2021 with a friend in an area where sex trafficking gangs operate.

"They stole her from me," Gallardo said in an interview with a local news website a few months ago.

"If she could hear me I would tell her that I love her and I'm still looking for her. Her mother did not abandon her," she added.

The authorities said they would investigate whether Gallardo's murder was related to her daughter's disappearance.

Other relatives of missing persons have also been murdered in Mexico, where more than 100,000 people are listed as having disappeared and even looking for them can carry significant risks.