When Jennair Gerardot found out her husband was cheating on her, she came up with a plan of revenge, one that would lead to a bloody murder-suicide and stun a quiet Pennsylvania town, authorities said Tuesday.

The victim was Meredith Chapman, 33, a woman with whom Gerardot’s husband was having an affair, police said. She was a lot like Gerardot — a successful, driven marketing professional in the Delaware area. She also happened to have worked with Gerardot’s husband at the University of Delaware.

After finding out about the affair, Gerardot plotted a “calculated attack,” police said. “There were emails and text messages indicating what she planned to do,” Radnor Township Police Superintendent William Colarulo said in a news conference Tuesday.

On Monday, Gerardot took a train from Delaware to Chapman’s new home in a tranquil residential neighborhood in Radnor, Pa., possibly wearing a wig in disguise, Radnor Township Police Lt. Christopher Flanagan said in the news conference.

Gerardot broke through Chapman’s front door, stopping to clean the shards of broken glass off the floor.

With her Taurus Tracker .357 revolver in hand, she waited for Chapman to get home. As soon as Chapman walked through the door, police said, Gerardot shot her.

Then, Flanagan said, Gerardot turned the gun on herself.

When police arrived in response to 911 calls, both women were lying dead near the kitchen.

Melissa DeJoseph, 40, who lives two doors down from Chapman’s residence, told the Philadelphia Inquirer she saw Chapman walking out of her Audi and into her house Monday evening just before she heard the loud sound.

“In my head, I was like, ‘Is that a gunshot? No, it can’t be a gunshot,’ ” she said.

Outside the bloody scene, police came across the man who brought the two women together — Gerardot’s husband, Mark. “My wife might be inside,” he told police.

Mark Gerardot, who lived with his wife in Wilmington, Del., was supposed to meet Chapman for dinner that night. When she didn’t shown up, he became concerned and went to her house in Radnor, police said.

The tragedy “rocked the world” of the township and the surrounding neighborhood, Flanagan said, describing it as a “tightknit community” with many children and families. “Nobody wants to see something like this happen in their neighborhood,” he said.

But it also shocked the marketing, political and higher education worlds in the Delaware area, realms in which the Chapmans and Gerardots both found some prominence.

Chapman had recently left her job at the University of Delaware and begun working as an assistant vice president of marketing and creative services at Villanova University.

A former broadcast journalist in Philadelphia, Chapman worked as a communications manager on Capitol Hill for Rep. Michael N. Castle (R-Del.), who served in the House from 1993 to 2011. At the University of Delaware, she worked as a senior marketing director and taught classes to students at the undergraduate, MBA and continuing education levels, according to her website. In 2016, she also unsuccessfully ran for a Delaware state Senate seat as a Republican.

She was married to Luke Chapman, a former member of the City Council in Newark, Del., and she wrote proudly on Facebook about his work. But she had recently moved into the three-story brick residence in Radnor alone and was no longer living with her husband, police said.

“Meredith was a beacon of light to anyone who was fortunate enough to meet her,” a spokesman for the Chapman family said in a statement to the News Journal. “She loved her family fiercely, was a compassionate friend and among the most talented and innovative professionals in her field. Her death was sudden and tragic, but will not define who she was to the thousands of people who loved her. Her family is devastated, heartbroken and requests privacy and respect as they grieve.”

Erik Raser-Schramm, chairman of the Delaware Democratic Party, released a statement Tuesday saying he was “devastated to learn of the tragic loss of a dear friend.”

“In the hours since receiving the news, it has been impossible for me to imagine our Delaware without someone so transcendent and committed to service,” he said.

“Everyone who knew and worked with Meredith is heartbroken,” the University of Delaware said in a statement to WHYY. “As a proud alumna of UD, her commitment to her work was exceeded only by her boundless energy. She believed earnestly in the power of communication to bring people together, whether to achieve their collective goals or simply to share their stories. We will miss her.”

Mark Gerardot, who worked as a creative director, reported to Chapman at the University of Delaware. The university told the News Journal he left the job there earlier this month.

The Gerardots had been married since 1993, according to Indiana State Library records, the News Journal reported. They lived and worked together in Indiana at a branding and package design agency called Gerardot & Co., co-founded by Mark.

Jennair Gerardot, who was in her late 40s, described herself on her website as a “confident, creative and resourceful” marketer with more than 16 years of experience. “The softer side of this highly-driven businesswoman also likes exploration and travel; and is an avid animal and nature lover,” she wrote.

She would often post photographs with her husband, holding hands on the beach walking their golden retrievers.

Her husband often posted photographs of her on his Instagram account. “My birthday present 24/7. I’m a lucky guy,” Mark wrote alongside a photo of his wife on Instagram in October 2015.

He also doted on his wife on his website: “On the personal side, my wife and golden retriever are the center of my universe and the reason I get up every morning.”

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