A man who fatally gunned down nine people outside a Dayton, Ohio, bar early on Sunday had long wrestled with mental illness that manifested itself in a fascination with tragedy, uncontrollable urges to unleash violence and deep suicidal thoughts, a former girlfriend said on Tuesday.

Though her account didn’t shed light on what drove 24-year-old Connor Betts to carry out Sunday’s attack, the woman who dated him for a few months earlier this year offered the most detailed portrait yet of a troubled young man obsessed with the darkest of thoughts.

“I have no idea what his motivation was. I will never know,” Adelia Johnson wrote in a 2,200-word recounting of the relationship, which she sent to some reporters and posted online.

“There wasn’t a hate crime. He fought for equality. This wasn’t a crime of passion. He didn’t get passionate enough. This wasn’t very premeditated. He wasn’t a thorough planner.”

The tone was set on their first date, she said, when Betts showed her a video of last year’s Pittsburgh synagogue shooting and narrated it play-by-play. Later, he steered conversations to talk about world tragedies and his suicidal thoughts.

“He trusted me with so much of his darkness that I forgot most of it,” Johnson wrote, adding that she brushed off much of what she heard. Talking about serial killers made sense as it was a theme in a Sinclair community college psychology class they both were taking.

A captivation with disaster and violence was offset by the sweetness of a “perfect gentleman” and joking about a desire to hurt others was seen as the coping tool of a man grappling with illness.

Johnson said she and Betts bonded over mental illness.

He told her he had bipolar disorder and might also have obsessive-compulsive disorder.

And she said he confided that while he loved guns, he didn’t believe those with mental illnesses should be allowed to have them.

Betts’ high school classmates said he was once suspended for compiling lists of students he wanted to rape or kill. And Johnson’s recounting of her relationship with him revealed two moments that stood out as “red flags”.

In March or April, on the road in Illinois for a gig with his heavy-metal band, she said a drunk and slurring Betts called her and said something about how “he wanted to hurt a lot of people”.

In May, Johnson said Betts was planning to leave a letter at the home of an ex-girlfriend that warned her: “You can’t outrun your past.”

That time, Johnson said, he tried to downplay it as a joke, but she knew it wasn’t. When she pushed him to explain, she said he spoke of “uncontrollable urges to do things”, including a time he set fire to an abandoned building. She said she knew she had to break things off, unable “to be his therapist”.

When Johnson got a text from a friend, who also knew Betts, after the shooting asking if she thought he could be the gunman, she didn’t think it was possible. Though he had problems with his parents, she knew him to like his sister, who was among those killed.

The gunman was killed by law enforcement less than a minute after launching his attack.