Jennifer Hudson excused herself from the courtroom in the murder trial of the man accused of gunning down her family ... deciding she did not want to see the grisly crime scene photos of her slain 7-year-old nephew.
Prosecutors displayed multiple photos of the blood-soaked body of Julian King ... who was shot twice in the head in 2008.
The man accused of the crime -- William Balfour -- remained inside the Chicago courtroom and reportedly appeared to cry when the photos were displayed.
Hudson's fiance, David Otunga, also remained inside the courtroom ... and took extensive notes about the crime scene.
Prosecutors believe Balfour murdered King -- along with Hudson's mother and brother -- in a horrific killing spree in October 2008. Balfour has plead not guilty to the murders.