The owner of a gunpowder plant convicted in an explosion that left two workers dead could soon walk free after a home invasion left the key witness against him dead.

Craig Sanborn, the owner of the Black Mag gunpowder plant that blew up in 2010, is seeking a new trial. And if he gets one, the case against him will be weaker — or could go away entirely.

"I'd have to regroup on everything," said prosecutor John McCormick. "It would be tough to go forward without one of the key witnesses."

David Oldham, whose testimony helped land Sanborn behind bars, was shot to death earlier this month. His death remains unsolved.

Oldham was the manager of the Colebrook plant when an explosion killed workers Donald Kendall and Jesse Kennett. He was the only survivor.

At trial, Oldham testified about the pressure Sanborn, of Maidstone, Vermont, put on workers to step up productivity to meet a large order that was due May 17 — three days after the explosion. He said Sanborn told him to keep the machines running and expedite any repairs that might be needed. He also testified about how Sanborn ignored advice to bunker each machine and move them farther away from each other and to have workers operate the machines remotely.

Oldham also testified about what was happening right before the explosion, when he could hear one of the workers banging on a metal machine with a pipe.

Oldham, in his office about 30 feet from the flashpoint, suffered serious injuries. He sued Sanborn and the gunpowder plant's parent company for $250,000 in damages and medical expenses. The case settled for an undisclosed amount in March 2014.

But Oldham, whom McCormick called him an "indispensable" witness, was found dead earlier this month at his home in Columbia, New Hampshire.

McCormick said Oldham's unsolved killing is "disconcerting." Senior Assistant State's Attorney Jeffery Strelzin said there are no new developments in the investigation.

Sanborn was convicted of manslaughter and negligent homicide and sentenced to 10 to 20 years in prison in November 2013. In June, the New Hampshire Supreme Court heard arguments in the appeal of his convictions and several justices seemed to latch onto his lawyer's argument that that there were too many potential causes of the explosion to home in on Sanborn as the perpetrator. Attorney Mark Sisti noted that Sanborn was attending a conference in another state when the plant exploded on May 14, 2010.

Sisti said he wouldn't speculate about his strategy if a new trial is granted.

"I'm just waiting for the Supreme Court to do the right thing and we'll go from there," he said.

Sanborn remains behind bars while his appeal continues. Prosecutors cited then-pending federal fraud charges pending in Maine in arguing that he posed a flight risk if released on an appeal bond.

Sanborn also was convicted last year of wire fraud for submitting false invoices to the town of Brownville, Maine, in connection with the development of another ammunition plant. He was sentenced to 28 months, which he must serve once he's released from prison on the state convictions.

Even though Oldham could not take the stand at a retrial, his testimony could still come into play.

Lawyers say the rules of evidence allow for admission into evidence of a prior transcript as long as the defendant or his lawyer had a chance to cross-examine the witness, but it's not like having a live witness.

"It's not as effective and compelling if the witness was a good witness," said defense attorney and former prosecutor Michael Ramsdell.

Ramsdell said a "plain, cold, typed transcript" doesn't convey a witness's demeanor, body language or tone when testifying. "This is why jurors are told, when a witness testifies, that you don't just listen to what they're saying. You observe the witness and make your own judgments about the witness's credibility."

"That just doesn't come across the same way on a printed page," Ramsdell said.