© Ron Antonelli/New York Daily News
David Tarloff after his arrest for the brutal murder of Kathryn Faughey.
Schizophrenic cleaver David Tarloff is arguing an insanity defense in the trial that he brutally murdered his therapist Kathryn Faughey.

Psycho slasher David Tarloff truly believed he was the Messiah following instructions from God when he set out to rob his first shrink in 2008, a defense expert witness testified in his murder trial Tuesday.

Tarloff's deluded plot to hold Kent Shinbach hostage to get money to rescue his infirm mother from a Queens nursing home was sanctioned by God, at least in his sick mind, psychiatrist Eric Goldsmith testified.

"That was the belief he was operating under," Goldsmith told jurors.

Tarloff stabbed and bludgeoned Shinbach's colleague Kathryn Faughey to death and nearly killed Shinbach but did not get money and fled the E. 79th St. office the doctors shared, only to be tracked down and arrested days after the Feb. 12, 2008 slaying.

But the schizophrenic accused killer is so mentally ill "he failed to appreciate his actions that night were wrong," Goldsmith said.

Goldsmith, who is expected to be on the witness stand for days, is the fourth to testify on behalf of Tarloff's insanity defense. Prosecutors and Faughey's family argue Tarloff knew his actions were criminal and he should be held accountable for the heinous killing.