Karen Lockyear said it still "seems unthinkable" that her friend, Mark Ernsting, is dead after the cancer researcher and professor was stabbed in a random attack while on one of his routine evening walks in downtown Toronto this week.

"Mark loved life. Besides his work as a scientist, he was an avid gardener, he sang in a choir, he went for walks all the time," Lockyear told CBC Radio's Metro Morning on Thursday.

Ernsting, 39, died after being stabbed multiple times in what police said may have been a robbery gone wrong around 9:30 p.m. ET on Tuesday night. Ernsting was out for his regular walk near Yonge Street and the Ryerson University campus.

Police later charged a 21-year-old man.

He always wanted to help people. - Karen Lockyear , friend of cancer researcher Mark Ernsting

The awful random violence that claimed his life, Lockyear said, is "shocking."

"You hear these stories and you go about your day, and you think it's terrible, but you don't think that it's a real person ... every victim is a real person," Lockyear said.

Ernsting's friends and families are now gathering around his husband, Rob Iseman, to provide support.

Lockyear described Ernsting as a gentle and loving person who was passionate about his work with the Ontario Institute for Cancer Research (OICR) and as an adjunct professor for Ryerson University.

"He always wanted to help people," she said.

Both the OICR and Ryerson mourned Ernsting's loss in statements released Wednesday. The cancer institute called the biomedical engineer "a talented researcher and a terrific person."

The university, where Ernsting worked as an adjunct professor, said it's "deeply saddened by this senseless, tragic event," and that it's working with police to keep the area safe.

Outside of work, Lockyear said Ernsting always left her smiling. She remembers him dropping by her suburban Scarborough home once just because he was biking in the area, and also had joking during a camping trip that not only had he brought shampoo, but conditioner, too. Lockyear said he was also a friend to her children, aged 5 and 8.

"It's always good to think about someone and smile," she said.

Toronto police arrested Calvin Michael Nimoh around an hour after the stabbing. He has been charged with second-degree murder and appeared in court on Wednesday.