Joshua David Lambert will spend the rest of his life behind bars as a convicted double murderer.

A jury found Lambert guilty on all counts, which include two counts of first-degree murder, kidnapping and several burglary and guns charges.

The jurors rejected Lambert’s insanity defense altogether. The prosecution presented evidence suggesting he committed the murders and kidnapping in the midst of a methamphetamine-induced psychotic episode.

The jury returned the verdict Thursday afternoon, after deliberating for about six hours.

Lambert, 32, wasn’t in the courtroom, but appeared from the jail on a large-screen TV with a video connection. Judge Vickie Churchill removed him from the court because of his continued angry outbursts, which culminated in a courtroom fight with guards.

Prosecutor Greg Banks said Lambert is virtually guaranteed to receive a life sentence, especially since jurors found that he committed a series of aggravating factors, which increase the sentence.

Lambert’s sentencing hearing hasn’t been set, but will likely be in the next month.

Lambert had been acting as his own attorney in the months following the Oct. 3, 2011 murders. He stabbed to death his paternal grandfather, George Lambert, tying up his great aunt and then stabbing to death his maternal grandfather, August Eugene “Sonny” Eisner. His grandfathers were both 80 years old and lived in separate residences on North Whidbey.