In what police are alleging was a 'calculated attack' Jennair Gerardot, 48, was likely wearing a disguise as she took a train to the quiet suburb of Radnor and broke into the home of Meredith Chapman, 33. Ms Chapman worked with her husband, Mark, at the University of Delaware.
Stopping to clean up the shards of broken glass from the front door, she waited for Ms Chapman to return home and shot her.
Moments before she attacked, she is believed to have text her husband the details of her deadly plan. She then turned the gun on herself.
'There were emails and text messages indicating what she planned to do,' Radnor Township Police superintendent William Colarulo said during a news conference.
'You had a man who was married who was having an affair with this other woman. The wife knew about it, and this was a calculated, planned attack.'
The women's bodies were found metres apart in Ms Chapman's home.
When police arrived, they found Mark Gerardot outside. 'My wife might be inside,' he told them.
Mr Gerardot was supposed to meet Ms Chapman for dinner that night. But when he'd received disturbing text he'd showed up at the home in Radnor.
Jennair and Mark had been married since 1993 and often posted photos together, expressing their love for each other.
'My birthday present 24/7. I’m a lucky guy,” Mr Gerardot wrote alongside a photo of his wife on Instagram in October 2015.
But it has since emerged that Ms Gerardot had sought marriage counselling before the attack, describing their marriage as 'on the brink of divorce.'
Less than two hours before she was killed, Ms Chapman posted on Instagram that she 'couldn't be more excited' after being hired as the vice president at Villanova University.
'Meredith was a beacon of light to anyone who was fortunate enough to meet her,' a spokesperson for the Chapman family told 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.'
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