Eighteen months after a Chelsea woman was sexually abused for almost 13 hours by a man who entered her home dressed as a firefighter on Halloween and tied her up at gunpoint, the 36-year-old testified yesterday that she feared the masked man would kill her.

“I knew as morning came, he either had to leave or get rid of me,” the woman said during more than three hours on the witness stand.

She would later learn that she had seen the man on trial for the felony attack — journalist Peter Braunstein — at the workplace they once shared.

Throughout the night of the attack, prosecutors say, he drugged her five times with chloroform purchased, via the Internet, after setting off smoke bombs in her apartment building’s hallway to trick her into opening the door.

Because she passed in and out of consciousness during the 13-hour ordeal, she said she didn’t know whether she had been raped. (An exam at the hospital later showed she hadn’t.) All she knew at the time was that she was naked except for panties and shoes the assailant put on her feet.

Mr. Braunstein had fled by the time she summoned the authorities.

She initially refused to permit police officers responding to a 911 call to enter her apartment, as her assailant had himself been in uniform when he broke in. She cried yesterday on the witness stand as she recalled the morning after.

Attorneys for Mr. Braunstein don’t dispute that the attack occurred or that it was “horrible, horrible,” in the words of defense attorney Celia Gordon. Nor do they dispute that their client is the man who brutalized the victim.

They say Mr. Braunstein’s actions that Halloween night were the culmination of years of illtreated mental illness. His defense team plans to show brain scan images to convince jurors he should be found not guilty.

“This trial isn’t about what happened on Halloween 2005,” Ms. Gordon said in her opening statement yesterday. “This trial is about why — why it happened.”

Ms. Gordon said her client is “someone whose brain just broke.”

Assistant District Attorney Maxine Rosenthal countered that Mr. Braunstein’s desire for revenge, not his mental illness, led him to attack the woman 18 months ago.

“New York had turned its back on Peter Braunstein,” Ms. Rosenthal told the jury in her opening statement. “He was angry, and it was time to strike back.”