ST. CLOUD, Fla. — The human remains recovered from the yard of a St. Cloud home are of Nicole Montalvo, who had stopped by there Monday night to drop off her son and hadn't been seen since, the Osceola County Sheriff said Sunday. 

The investigation into the disappearance of Montalvo now has turned from a missing person's case to a murder investigation, Sheriff Russ Gibson said during a brief news conference.

Montalvo's estranged husband, Christopher Otero-Rivera, and his father, Angel Rivera, were arrested Friday night on charges unrelated to the Montalvo case. At the time, Sheriff's officials called them persons of interest.

By Sunday afternoon, a charge of premeditated murder had been brought against both Otero-Rivera and Rivera.

During a second brief news conference later that night, Gibson said a warrant search at a second home on Henry J Avenue turned up more human remains. That home was also owned by the Rivera family, Gibson said. Based on that and other evidence, detectives established probable cause to charge Otero-Rivera and Rivera with first-degree murder.

"We want to implore people out there that this investigation is by no means over. ... We're just scratching the surface with the information we've uncovered so far," Gibson said.

At Broadway Pizza Bar in Kissimmee, a sign on the door said the restaurant was closed for the evening "in remembrance of our server Nicole Montalvo."

"No matter how minute a role you may have played in this heinous murder, we are closing in on all of you. (To) every one of you, there is no rock you can hide under, no pond we can't drain to find the evidence we need to substantiate a guilty verdict in this case," Gibson said.

Montalvo's last known location was at the home on Hixon Avenue, where she'd gone Monday night to drop off her young son to his father and grandparents. 

By Wednesday, her parents had reported her missing. 

Authorities began searching the property Thursday, and less than 24 hours later found what Gibson described as possible human remains in the backyard.

On Sunday, deputies could be seen digging in the woods beyond the house on the 5-acre Hixon Avenue property. Authorities also drained a pond behind the house Saturday and Sunday.

Otero-Rivera faced a judge Sunday morning and was being held without bond at the Osceola County Jail. Rivera was transported to a hospital after his arrest after he complained of shortness of breath, according to Osceola County Sheriff’s Lt. Justin Boutilier. Rivera’s first appearance in court was scheduled for Monday but is dependent on his release from the hospital.

Gibson said there will be a candlelight vigil held in Montalvo's honor at the St. Cloud waterfront Monday night, and Gibson will be there.

Previous charges against Otero-Rivera

Investigators said Otero-Rivera has a history of domestic violence against Montalvo. According to an Osceola Sheriff's Office affidavit dated October 4, 2018, Otero-Rivera, with help from another woman, kidnapped and attacked Montalvo after luring her under the pretense of needing a ride because of a dead truck battery.

Montalvo was taken to an isolated road in Poinciana, where she was thrown to the ground, attacked, and threatened over texts she sent to a friend and for "taking his (Otero-Rivera's) son," the affidavit said. About $40 and debit cards that Montalvo were missing after the alleged attack were found in Otero-Rivera's wallet, said St. Cloud Police, investigators wrote.

Multiple felony charges were filed, but according to court documents, the state declined to prosecute the more serious charges of kidnapping with intent to inflict bodily harm and robbery during a plea deal. And the judge withheld adjudication on Otero-Rivera for the charges of tampering with a witness to hinder communication to law enforcement, unlawful possession of a stolen debit card, and battery.

Otero-Rivera was under house arrest and probation at the time Montalvo disappeared.

Read more about the details of that incident here