ST. CLOUD, Fla. — Nicole Montalvo's mother-in-law has been charged with key evidence tampering, the Osceola County Sheriff's Office announced on Friday.

Wanda Rivera, 59, is also facing charges of making false statements to investigators on October 21, Sheriff Russ Gibson told Spectrum News 13.

Rivera is the mother of Christopher J. Otero-Rivera, who along with his father, Angel Luis Rivera, are charged with first-degree murder of Montalvo.

“(We'll) turn over every stone, drain every pond, if we need to, to get to the bottom of this barrel," Gibson said.

Gibson said investigators are shifting through numerous leads and that the investigation is still ongoing.

"We will be the voice for the voiceless," Gibson said of his office's investigation.

Gibson said that there are other people his office is looking into in the death of Montalvo, but did not go further as to who they might be.

“There are others out there, and they know who I am talking to. We know who you are. We’re about to show up at your doorstep too," the Sheriff said.

Montalvo went missing Monday, October 21, after she dropped off her son with Otero-Rivera and his grandparents in St. Cloud.

However, her remains were found at the St. Cloud home of her father-in-law and estranged husband days later.

Montalvo and Otero-Rivera were in the middle of a divorce and had a history of domestic violence, records show.

In early October, she wrote to the judge asking they drop an order of protection against her husband. 

In that letter she also wrote, “I also have a lot of trust in my in-laws, (because) no matter what happens they are always there for me and our son.”

Currently, Rivera is being held on a bond of a $100,000.