A Calgary man accused of sexually assaulting vulnerable teens has now been charged with child pornography and drug charges.

On March 13, Robert Wortman, 62, was charged with sexual assault after an investigation into two separate incidents involving young men were reported to police.

Following the initial arrest, police executed search warrants at the accused's apartment and collected additional evidence.

On Thursday, the Calgary Police Service said Wortman has now also been charged with:

trafficking of a substance.

making child pornography.

distributing child pornography.

possessing child pornography.

accessing child pornography.

luring.

sexual assault.

forcible confinement.

sexual exploitation.

Multiple victims came forward

In January, a 17-year-old male reported to police that he had been sexually assaulted. Police believe the perpetrator saw that the youth was vulnerable and offered him drugs.

Police say the teen accepted what he thought was crystal meth, but it is believed he was also given GHB to incapacitate him before he was sexually assaulted.

Wortman was arrested on March 12 after allegedly chasing a second man with a knife as he fled an apartment.

The 19-year-old man, who had gone to Wortman's home in the 1000 block of 16th Avenue S.W., escaped unhurt, police say.

Police say a third man, another 17-year-old, came forward in May after the arrest alleging he was sexually assaulted and forcibly confined in the Wortman's apartment in late 2016.

A former member of the Calgary Homeless Foundation's board of directors, Wortman was voted off the board hours after it was revealed that he had been charged with sexual assault in March.

Wortman has also held a number of Indigenous relations positions, including as a former adviser to the former chief of the Assembly of First Nations Phil Fontaine.

He currently works as a consultant on energy projects for First Nations communities.

Wortman was scheduled to appear in court in Calgary on Thursday.