Florida police charged a 25-year-old man with first-degree murder after they found human remains they believe belong to a missing family in his fire pit.

Rory Atwood was arrested in Pasco County, Florida Saturday, the Pasco Sheriff's announced at a press conference, recounting a complicated investigation into an incident they believe occurred sometime between June 12 and June 13.

Pasco Sheriff Chris Nocco said the investigation is ongoing, but the case is likely linked to the missing persons case of Rain Mancini, 26, Phillip Zilliot II, 25, Karma Zilliot, 6, and Phillip Zilliot III, 5.

According to the criminal complaint, Atwood told detectives he was in an altercation with the two adults, they struggled over a gun, and they were shot to death. He then said he used "adrenaline" to drag them to a fire pit on his property.

Atwood pleaded not guilty Monday, and is being held without bond, court records show. The public defender appointed to his case declined to comment.

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Cadaver dog finds 'small skeletal remains'

The Pasco Sheriff's Office said Friday it was looking for the family last seen June 12, according to a Facebook post.

Officers received information from secondary sources raising concerns about Atwood's possible involvement, according to the criminal complaint. But when police arrived at Atwood's home in Hudson, Florida, he allowed police to search the property and they did not find anything suspicious.

Upon a later search, a cadaver dog found what "appeared to be a small skeletal remains" with soft tissue in a fire pit measuring approximately 10-feet in diameter, records show.

Forensic investigators also found apparent human long bone fragments and two apparent human vertebrae, according to the complaint.

Atwood said he thought the parents killed and burned their own children

Atwood later explained to police he evicted Mancini and the Zilliots on June 1 when they did not pay rent, and they came back unexpectedly on June 12.

Atwood also said Phillip Zilliot II came into his bedroom with a knife, and the two fought, while Mancini threatened one of Atwood's relatives with a knife.

The three adults struggled over the knife and a gun, Atwood told police. In the process, Mancini was shot multiple times in the head and torso and Phillip Zilliot II was shot twice in the head, Atwood said according to the complaint.

Atwood told detectives he suspected Mancini and Phillip Zilliot II killed their two children, as the fire was already going on the property, and he did not see the children after the altercation with their parents. However, Atwood knew the children were in the fire pit, according to the complaint. Atwood also reported burning a couch from his living room, which contained blood evidence, and the firearm used in the altercation.