Bryan Kohberger abruptly agreed to a plea deal — essentially ending his murder case before trial — just days after his sister was added as a witness … TMZ has learned.

According to documents obtained by TMZ, Kohberger’s sister, Amanda, was included on the prosecutor’s witness list … which could have meant the confessed killer would have had to face off against her in court, but he dodged that possibility. Amanda was the only immediate family member on the list.

Kohberger had reportedly been charged with misdemeanor theft for allegedly stealing her cell phone in 2014.

On July 2, Kohberger pleaded guilty to fatally stabbing 4 University of Idaho students inside their off-campus home in Moscow in November 2022.

While recounting the events to ABC News, Idaho State Police Lt. Darren Gilbertson said police found Ethan Chapin‘s butchered body on a bed in his girlfriend’s room with his blood leaking through the interior wall and out of the side of the house. The grisly image was originally captured in a photograph that will surely live on in infamy.

Gilbertson also said Chapin’s girlfriend, Xana Kernodle, was found stabbed to death on the floor in the same room.

He went on to say Kohberger’s two other victims — Kaylee Goncalves and Madison Mogen — were found slain in bed together in another room, noting that Kaylee had unique injuries with a horizontal pattern.