The man accused of fatally stabbing cancer researcher Mark Ernsting last month is now facing an upgraded charge of first-degree murder.

Calvin Michael Nimoh, 21, had his charge upgraded during a court appearance on Thursday.

The lead detective in the case, Det. Paul Worden, said Thursday that the charge was upgraded after investigators uncovered evidence of forcible confinement in the incident. The new evidence came to light during interviews with eyewitnesses and while reviewing security camera footage from the area.

Police still consider the stabbing "a random attack, a crime of opportunity," Worden told CBC News, adding that he doesn't expect further charges to be laid in the case.

However, it is his understanding that there are more witnesses to the incident who have yet to come forward. He is asking them to contact police.

Nimoh was initially charged with second-degree murder after Ernsting, 39, died following an attack near Ryerson University on the evening of Dec. 15.

Ernsting was out for one of his regular evening walks when he was attacked near 38 McGill St., just east of Yonge Street. He was stabbed multiple times.