A coroner ruled that William Mussack had been poisoned with acepromazine, an animal tranquilizer
Dayna Jennings
Credit: Adams County, Colorado, Sheriff's Office/ AP

A Colorado woman was sentenced to life in prison without parole earlier this week for poisoning her father with an animal tranquilizer and then covering his remains in concrete in a crawl space in their home.

Dayna Jennings, 45, was found guilty of first-degree murder and tampering with a human body in July for the poisoning death of her 69-year-old father William Mussack.

Mussack had been missing for a month before law enforcement discovered his decomposing body encased in a layer of concrete in the basement of their Federal Heights home in January 2018. His body was also covered with trash, household garbage and old photos, according to an Adams County District Attorney’s Office press release obtained by PEOPLE.

A coroner ruled that Mussack had been poisoned by acepromazine, an animal tranquilizer.

”Jennings repeatedly misled the family after they became concerned about Mussack, describing everyday routines as if things were fine,” Chief Deputy District Attorney Rhoda Pilmer said during the trial. “All the while, she was scheming about how to get rid of her father’s body. She researched the drug, ordered it, received it. All of those were opportunities to stop and ask herself, ‘Am I really going to poison my father?’”

Chief Deputy District Attorney Brett Martin said that after Jennings poisoned her father, she texted a friend: “Life is so different now I feel so much better.”

William Mussack
William Mussack
| Credit: Federal Heights Police

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The case came to light on Dec. 28, 2017, when Mussack’s brother contacted police asking for a welfare check on his brother because he hadn’t heard from him since Dec. 5 and couldn’t reach him, according to an arrest affidavit obtained by PEOPLE.

When questioned by police at their home, Jennings allegedly said Mussack didn’t live there and that he had lost his phone, the affidavit states.

The next day, Mussack’s brother called police again, saying he still had not heard from him, prompting police to visit Jennings again.

An officer who searched the home on Dec. 29 said he smelled something rotting and that the house smelled like sewage, according to the affidavit. He also said he saw a pile of women’s clothing on Mussack’s bed in his room, which looked like it hadn’t been occupied in weeks, the document states.

The officer returned to the home the next day and noticed construction materials that had been stacked on the driveway had been moved, but that Mussack’s vehicles were in the driveway, according to the affidavit.

Jennings allegedly told the officer that her father’s cell phone and rent money had been taken and that he had gone to the mountains with his girlfriend.

When the officer asked to search the home, Jennings allegedly said no.

Mussack’s girlfriend told police the last time she heard from him was on Dec. 8, when he said he would attend a Christmas party with her the next day, but failed to show up, according to the affidavit.

On Jan. 10, when police executed a search warrant at Jennings’ home, they found the man’s remains encased in concrete in a crawl space in the basement.

In an interview that day with police, Jennings allegedly confessed after investigators received a text message informing them of what they had found at the house, the affidavit states.

Jennings allegedly admitted “to pouring concrete in the crawlspace where the human remains were located,” according to a search warrant affidavit.

Prosecutors said the concrete had been purchased at Home Depot in late December.

Mussack’s son also told police that his father relayed to him that he had passed out for 15 hours after his daughter gave him a hamburger on December 7, 2017, and that he’d said, “she must have drugged me.”