The Saskatchewan judge presiding over Gerald Stanley's murder trial today advised jurors on how to navigate the contradictions in testimony they have heard this week.

"Common sense tells you that if a witness says one thing in the witness box, but has said something quite different on an earlier occasion, this may reduce the value of his or her evidence," Chief Justice of Saskatchewan's Court of Queen's Bench Martel Popescul told the five men and seven women on the jury.

Stanley, 56, is on trial in Battleford accused of fatally shooting Colten Boushie, 22, in 2016. He has pleaded not guilty.

Boushie was fatally shot on Stanley's farm near Biggar, Sask., in August 2016. (Facebook)

Boushie was shot after he and four friends from the Red Pheasant First Nation reserve drove onto Stanley's rural property near Biggar in a grey SUV on Aug. 9, 2016.

'I lied about that'

One of the other SUV passengers, Cassidy Cross-Whitstone, 18, testified this week that he previously did not tell the truth about trying to break into a truck on another property near the Stanley farm and about how much he'd had to drink that day.

"I lied about that," said Cross-Whitstone, adding that he was afraid of losing his driver's licence.

Another SUV passenger, Belinda Jackson, 24, said in a previous statement that the only person with a gun at the farm that day was a woman outside the SUV.

But on Thursday, she told jurors she saw Stanley shoot Boushie twice in the head while he was sitting in the SUV.

"It doesn't make any sense," said defence attorney Scott Spencer of that and other inconsistencies.

Defence to call 'a number' of witnesses

Popescul told jurors they should not take previous statements as evidence unless the witnesses admitted on the stand that their prior statements were untrue.

Crown prosecutor Bill Burge called his last witness Friday.

Greg Williams, an RCMP forensic firearms expert, said the handgun that killed Boushie — and that one witness saw Stanley holding — did not show signs of "mechanical malfunction."

The RCMP took this photo of the semi-automatic pistol that is believed to have killed Colten Boushie. (RCMP)

Stanley's son Sheldon told jurors earlier this week that his father said the gun went off accidentally when he was trying to scare off Boushie and the others.

Spencer called his own firearms expert Friday who testified that the gun was working properly.

Spencer said he would be calling "a number" of witnesses next week.

It is not known whether Stanley will testify.