A 28-year-old Pennsylvania man has been charged with criminal homicide and kidnapping in the death of his mother, whose body was found in a shed outside a Philadelphia behavioral center.

The Bucks County District Attorney’s Office said that Sean Rivera is accused of drugging 72-year-old Carol Clark with fentanyl and then driving her 30 miles away to Philadelphia, where he shot and killed her, according to WPVI.

Rivera and Clark lived together in Falls Township, the district attorney’s office said.

Falls Township police began an investigation on Sunday when Rivera’s brother contacted them, the Philadelphia Inquirer said. He said Rivera had texted him Sunday morning with a message that read “911,” and when he arrived at the home, Rivera said their mother “got sick and passed away.”

Later, however, he said that she hadn’t died but had a heart attack and was in a hospital in Philadelphia, although he refused to tell his brother which hospital. The brother checked with multiple hospitals but none had seen Clark.

In an interview with police, Rivera said his brother was right to be concerned about their mother but refused to say why, although he did say that he woke up Sunday morning to find her gone.

Police obtained a search warrant for the house and found two guns with receipts indicating Rivera bought them and a Home Depot receipt for two padlocks, although they only found one padlock.

Under further questioning, the Inquirer said, Rivera said that he laced his mother’s iced tea with fentanyl, leaving her in a “conscious but lethargic state.” Then, the affidavit says, he drove her to the Northeast Community Center for Behavioral Health in Philadelphia and shot her five times. He used bolt cutters — detectives found them in his vehicle — to cut the padlocks off the shed at the center, put his mother’s body inside, and used one of the padlocks he bought at Home Depot to secure the door.

Investigators found Clark’s body at about 1 a.m. Monday, WPVI said, using a key Rivera gave them.

A nearby resident told WPVI he heard gunshots early Sunday morning between 2 a.m. and  3 a.m.

Detectives have not revealed a possible motive.

Rivera is being held without bond.

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[Featured image: Sean Rivera/Falls Township Police Department and Carol Clark/handout]