Gregory Nisbet, the Portland landlord whose duplex on Noyes Street burned last Nov. 1, killing six young adults, pleaded not guilty Friday to six charges of manslaughter and four misdemeanor code violations in Cumberland County Unified Criminal Court.

Nisbet, who spoke in court only to confirm his identity to Justice Thomas Warren before saying “not guilty” to the charges, was released on his own recognizance after the hearing.

Wearing gray slacks, a dark coat and blue tie, Nisbet left the courtroom hastily before a brief recess.

If Nisbet is convicted, it would be the first time in Maine that a landlord was successfully prosecuted for manslaughter in the death of a tenant because of negligent operation of the building, said Deputy Attorney General Lisa Marchese, who is prosecuting the case.

“The state is proceeding on the theory that Mr. Nisbet failed to be aware or consciously disregarded all of the problems with the apartment building that resulted in all of the victims’ deaths,” Marchese said in a brief news conference following the court appearance. “It would be precedent in the state of Maine. However, if you look at other states, including New York and Rhode Island, there’s been successful prosecutions for the same conduct.”

A conviction would not necessarily require Nisbet to go to prison, but the state will push for that.

The Cumberland County grand jury indicted him July 10 after plea negotiations between his attorney, Matthew Nichols, and the office of Cumberland County District Attorney Stephanie Anderson collapsed when Nisbet refused to accept taking responsibility for manslaughter. Anderson’s office had given Nisbet a chance to plead to fewer counts of manslaughter and would have recommended a lesser punishment than what he could face if convicted in court.

A person is guilty of manslaughter if he recklessly or with criminal negligence causes the death of someone else. It is punishable by up to 30 years in prison and a $50,000 fine.

The fire killed Steven Summers, 29, of Rockland, Maelisha Jackson, 23, of Topsham, and Chris Conlee, 25, of Portland, who were visiting the house, and David Bragdon Jr., 27, Ashley Thomas, 29, and Nicole Finlay, 26, who lived there.

A real estate broker and landlord of 20-24 Noyes St. and at least two other properties in Portland, Nisbet has been accused in at least four wrongful death lawsuits filed by victims’ families of offering individual rooms for rent at that building without making the life-safety upgrades that are required to protect tenants in a rooming house.

In addition to the manslaughter charges, Nisbet was indicted on four misdemeanor code violations for allegedly not having working smoke detectors, clear stairwells and a second means of escape from an upstairs bedroom.