A 28-year-old man has been arrested on suspicion of murdering a San Francisco engineer who designed wheelchair accessories to help people with mobility issues, a source close to the investigation told The Chronicle.

Bart Kylstra, 52, the CEO of Rio Mobility, was found dead Wednesday night in a mixed-use building on the 1000 block of Market Street, according to the San Francisco Police Department.

On Thursday, Kuk Kim was booked into San Francisco County Jail on suspicion of murder, multiple counts of robbery and assault with a deadly weapon.

Kim, on his social media pages, lists himself as the chief operating officer of Kylstra’s company. The Chronicle’s source said investigators believe Kylstra was beaten to death when he confronted Kim about extorting products from the company. The suspect will be arraigned Monday afternoon.

Those close to Kylstra described him as a kind and loyal friend and family man.

He moved to San Francisco in 1991, and 11 years into a tech career he left to create the company Daedalus Wings, which was later renamed Rio Mobility. Kylstra’s company built equipment that could be attached to a wheelchair to ease the challenges of going up hills.

“He is a gem — a rare beauty — and a loss to all of us who knew him,” said Katryn Wiese, Kylstra’s girlfriend.

Kylstra loved San Francisco, an adopted home as is the case for so many city residents, and he gave personal tours to friends who visited, Wiese said.

Though he was often quiet, Kylstra was described by family and neighbors as kind, attentive and a “people person.”

“He was well dressed, and he seemed like a nice guy,” said Joe Castellano, a 24-year resident of the apartments in the mixed-use building that also housed Kylstra’s office.

The Rio Mobility founder often worked late into the night and on weekends as he tried to secure more funding for the wheelchair accessory company, according to family. Kylstra tinkered with designs and spent much of his time trying to improve the world around him.

He was passionate about applying his skills to help people with disabilities better navigate tricky terrain. This inquisitiveness also extended to thinking of ways to construct auditoriums with better acoustics as he waited for concerts, or building a quieter vehicle after being woken up by loud garbage trucks in the middle of the night.

In his downtime, Kylstra redesigned a boat and frequently drove up to the Sacramento Delta on weekends to spend time on the water. His fix-it mind-set applied to every part of his life — even in trying to understand problems his family and friends faced.

“Despite the natural flaws we all have, he was quick to look past these, to seek out the stories in our lives that led to these behaviors,” the family said in a statement to The Chronicle.

Kylstra is survived by his girlfriend, mother and eight siblings.

Gwendolyn Wu is a San Francisco Chronicle staff writer. Email: gwendolyn.wu@sfchronicle.com Twitter: @gwendolynawu