A Manhattan jury deliberated for less than four hours yesterday before finding a former fashion journalist guilty of kidnapping and sexually molesting a colleague after forcing his way into her Chelsea apartment while dressed as a firefighter.

By convicting Peter Braunstein on felony charges that include burglary, robbery, and sexual abuse, the jury rejected his defense that he was too psychotic to be found criminally responsible for drugging the woman with a chloroform-soaked rag, then holding her hostage for more than 13 hours beginning on October 31, 2005.

Braunstein — who showed no reaction as the jury foreman pronounced him guilty — never disputed that he had committed the acts the prosecution alleged over the course of the three-week trial. His attorneys blamed years of poorly treated mental illness and tried to sway jurors with images of Braunstein’s abnormal brain.

The jury found Braunstein not guilty of arson for a fire he was accused of setting as a ruse to induce the victim to open her apartment door.

The lead defense attorney, Robert Gottlieb, said he isn’t optimistic that Braunstein will receive mental health treatment after he is sentenced on June 18. He faces up to 25 years in prison.

“The law has never understood how to deal with people who do horrific acts and who are also mentally ill,” Mr. Gottlieb said. “We’ve treated them like lepers — we always have — and the law has not changed since the mid-1800s in recognizing that if you are mentally ill, the solution isn’t just to throw you in a cage.”