Bryan Kohberger Defense Theory On Who The 'Real' Killers Are Shot Down By Judge

Bryan Kohberger's defense has to go back to the drawing board ... after the judge in his criminal case denied his legal team's efforts to point the finger at four other suspects.

Kohberger is gearing up for a trial this summer after being accused of murdering four University of Idaho students ... and he was planning to argue someone else was the real murderer.

But in legal docs, obtained by TMZ, the judge blocked Kohberger's defense team from presenting evidence to the jury alleging someone other than Kohberger could be the true killer, blasting their evidence as "wild speculation" and "entirely irrelevant."

Kohberger's life is on the line here ... prosecutors are seeking the death penalty if he's found guilty of murdering Xana Kernodle, Ethan Chapin, Kaylee Goncalves and Madison Mogen.

The judge said there was no evidence connecting the people Kohberger claimed could be the murderers to the crime scene.

It's unclear who Kohberger claimed could have been behind the murders ... and now it's unlikely the public will ever know their identities.

The judge also laid out the timeline for Kohberger's upcoming trial ... jury selection is set for Aug. 4 and Aug. 18 marks the beginning of opening statements.