A Pennsylvania man diluted his mother's iced tea with fentanyl and drove to a storage shed where he fatally shot her and left her body covered in a tarp, court documents allege.

Sean Rivera, 28, allegedly told his brother, Adam Clark-Valle, their mother died and was in a Frankford hospital, but Clark-Valle couldn't find her in any hospital or in their Bucks County home and called police, according to the criminal complaint.

The entire time Clark-Valle and police searched for Carol Clark, a 72-year-old wheelchair user, she was in a storage shed about 25 miles away in Philadelphia, the complaint reads.

Rivera told responding officers that he picked up food for his mother and bought fentanyl "specifically" for her, according to the complaint.

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sean rivera mugshot

Sean Rivera, 28, is accused of killing his 72-year-old mother in Pennsylvania. (Buck's County District Attorney's Office)

"Rivera noted Clark was conscious but in a lethargic state from the fentanyl" as he drove her to a building in Philadelphia, where he wheeled her to a shed in the back of the property, the complaint alleges. 

Rivera cut the shed's padlock with bolt cutters, pushed her inside, allegedly shot her five times and locked the shed with a new padlock, according the complaint.

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That was around 2 a.m. and 3 a.m. Sunday, which the complaint notes was Clark's birthday, and Rivera texted his brother, "911," later that day and said their mother got sick and died.

Rivera's brother expressed concern about their mother's well-being to his brother when Clark didn't reply to his happy-birthday texts.

4371 Waln St, Philadelphia, PA 19124

Carol Clark was allegedly killed and left in a shed behind this building in Philadelphia. (Google Street View)

Rivera allegedly replied, "I don't know," and said multiple times that his brother "should be concerned," the complaint says.

Police tracked Clark's cellphone location and ultimately found body in the shed, according to the complaint.

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Falls Township police executed a search warrant on the home where Rivera and his mother lived. They confiscated two guns in the upstairs bedroom drawer with receipts made out to Rivera and a Home Depot receipt for two padlocks, the Buck's County District Attorney's Office said.

4371 Waln St, Philadelphia, PA 19124

Carol Clark was allegedly killed and left in a shed behind a building formerly known as Frankford Friends on Waln Street in Philadelphia. (Google Street View)

At the crime scene, police also found shell casings near the shed, according to the district attorney's office.

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Rivera was arrested and charged with criminal homicide, kidnapping to facilitate a felony, kidnapping to inflict terror or injury, aggravated assault, possession with intent to deliver a controlled substance, possession of an instrument of crime, possession of a weapon, false imprisonment, unlawful restraint and recklessly endangering another person.

According to the district attorney’s office, Rivera was booked into the Bucks County Correctional Facility without bail.