EVERETT — A Snohomish County Superior Court judge Thursday declined to dismiss charges against a Lynnwood man accused of trying to kill his ex-wife in a fiery 2014 attack.

Declaring a mistrial was appropriate last month after a deputy prosecutor’s questions prompted a fire investigator to testify that he believed the blaze at David Morgan’s home was intentionally set — an opinion that hadn’t earlier been disclosed to the defense, Judge Joseph Wilson ruled.

But granting a defense request Thursday to dismiss all charges wouldn’t serve justice, the judge said.

“I believe Mr. Morgan can be given a fair trial,” Wilson said.

Morgan is charged with attempted first-degree murder, arson and assault. He’s denied any wrongdoing.

The case began with a fire at his home on Nov. 16, 2014.

Morgan, 56, said he’d fallen asleep in front of the television and awoke to somebody striking him on the head. He told investigators about crawling from the burning home, believing his ex-wife, Brenda Welch, was behind him.

She was found unconscious in Morgan’s garage with burns to her neck and chest and a fractured skull. The injured woman smelled strongly of gasoline.

Welch had gone to Morgan’s house to pick up their daughter, but he’d earlier taken the girl to his mother’s home. His car reportedly was packed with family photographs, keepsakes and income tax returns.

Prosecutors allege Morgan planned to kill Welch over money. He reportedly didn’t like paying monthly child support and objected to handing over part of his retirement.

Public defender Donald Wackerman on Thursday accused deputy prosecutor Paul Stern of deliberately surprising the defense at trial.

The defense had been told fire investigators would testify that the blaze’s cause was “undetermined,” that no accidental cause had been discovered and that arson couldn’t be ruled out. Under questioning from Stern, however, one investigator said he believed the fire was deliberately set.

“This is not a mistake and it is shocking to attempt to cast it as one,” Wackerman said.

Stern filed an affidavit with the court Thursday, insisting that he’d simply gone too far in the heat of battle.

“The Court should not wrongly attribute to malice what is truly due to stupidity,” he wrote. “I was stupid. I was sloppy. I was unfocused. The jury heard an opinion which was not intended to be inquired of and was not intended to be offered.”

Wilson said he was not convinced it was a simple error, in part because Stern has decades of trial experience and is “beyond competent.” The judge said he was more inclined to believe Stern’s line of questioning was a response to testimony Wackerman had earlier introduced, and “an attempt to, I don’t know what, show the defense something.”

The judge said he will consider imposing other sanctions “as I deem just and appropriate” at a later date.

Meanwhile, he scheduled a new trial for Morgan for later this month.

Scott North: 425-339-3431; north@heraldnet.com. Twitter: @snorthnews