A convicted sex offender was arrested and accused of raping and murdering a great-grandmother during her walk along a trail near her Oil City, Pennsylvania home, prosecutors said.

Marcy Suzette Nellis, 76, was reported missing on March 27, which sparked a multi-jurisdiction, 12-hour search that included over 100 trained first responders until they found her body the next day along a bike trail near the Clarion University Venango Campus along the Alleghany River, the Oil City Firefighters union said on Facebook. 

A week later, law enforcement arrested David Allen Bosely, who was charged with homicide, rape by forcible compulsion, aggravated indecent assault, kidnappings and abuse of a corpse, the Venango County District Attorney's Office announced on Thursday.

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Nellis' cause of death was asphyxiation due to manual strangulation, and the victim was sexually assaulted, according an autopsy conducted in Erie County. 

Bosely "became an immediate person of interest" from evidence collected, including a rape kit and shoe impressions found at the crime scene, prosecutors said.

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"Additional photographs included areas of dense brush and debris along the hillside leading to the Allegheny River where Nellis was subsequently located," local news outlet Explore Venango reported based on the criminal complaint.

Surveillance was immediately set up around the suspect's home over the weekend, and Bosely was in custody by Thursday.

"The Erie crime lab worked through the weekend, prioritizing this investigation for the safety of our community," the Venango County DA's Office said in a press release.

He reportedly denied "touching that woman" and having "anything to do with" Nellis' death while talking to police, Explore Venango reported.

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Bosely was previously convicted of aggravated indecent assault attempted rape in 2000, according to state records, and required to register as a sex offender. 

A judge reportedly denied bail for Bosley, who's being held in the Venango County Prison until his next scheduled appearance on April 19.

Nellis' obituary said she was a longtime member of Good Hope Lutheran Church, active in church activities and enjoyed playing bridge "with the ladies at the Belle Lettres Club, living a healthy lifestyle and walking outdoors."

"Above all, Suzette loved spending time with her grandchildren; family always came first throughout her life," her obituary says. 

She was married to Jerry Nellis, Jr. for 57 years, and had four grandchildren and one great-granddaughter.

"At no point did responders give up hope and everyone came together and worked as a well-oiled machine throughout the entire search," the Oil City firefighters union said in a statement on Facebook.

"Please take this time look out for one another and seek support if needed in this tragedy. Finally, please keep the family of Marcy Nellis in your thoughts and prayers during this difficult time."