A Red Deer, Alta. teen charged with sexually assaulting numerous other teens involved with scouts and cadets over a period of years brandished a knife during one of the incidents, court heard Wednesday, as the trial began.

A 16-year-old witness, one of several to testify at the multi-day trial, sat quietly as video of an interview he gave Red Deer police last July played for the courtroom.

The witness was sexually assaulted a total of four times between 2011 and 2015, according to the Crown, including once during a Scouts Canada camp, once at Rexall Place in Edmonton, once at the accused's home, and once during a Cadets Canada camp.

The witness said the accused sexually touched him and masturbated in front of him.

In one of the assaults, the Crown said the accused showed the witness a knife and in another instance there was a verbal threat of a knife.

The Crown plans to call five complainants, both male and female.

A teenaged girl also tearfully testified Wednesday, saying she woke up while on a cadet trip a few years ago to find the accused with his hand up her shirt and exposing himself to her.

The accused, who was 17 at the time of his arrest, cannot be named under the Youth Criminal Justice Act.

He was involved with Scouts Canada between 2007 and 2012, and with Cadets Canada between 2011 and 2015, according to police.

The trial is scheduled to continue on Friday and then on Monday and Wednesday next week.