WORCESTER – Throwing out the more serious charge of first-degree murder, a jury Monday found Howard F. Penn guilty of voluntary manslaughter for fatally shooting a man at the Albion rooming house two years ago.

The 12-member jury, which deliberated for close to three hours Monday morning, based its decision on the case that the former security guard shot 52-year-old Lloyd Worster in self-defense but used excessive force in doing so.

Mr. Penn, a 56-year-old resident of Worcester, could face up to 20 years in prison for the manslaughter conviction, as well as shorter sentences for the lesser charges of possessing a gun and ammunition without a firearm identification card. The jury on Monday also found him guilty of those charges.

Mr. Penn, who is being held without bail, is to be sentenced Wednesday by Judge David Ricciardone.

The family of Mr. Worster, who worked as a handyman at the 765 Main St. rooming house, exited the courtroom quickly after Monday’s verdict. In an elevator, his daughter Nicole Worster expressed anger over the jury’s decision.

“It’s absolutely ridiculous,” she said, adding that Mr. Penn should have been convicted of murder. “Anyone who watched the video could see … he (expletive) shot him in the back.”

A surveillance video of the incident shown at the trial appears to show Mr. Penn firing a single shot as Mr. Worster walked away.

Mr. Penn’s lawyer, James B. Krasnoo, said after the verdict he believed jurors were swayed in part by the “nature and character of the deceased,” the hostile history between Mr. Penn and Mr. Worster, and the testimony of witnesses.

“He was not a nice man,” Mr. Krasnoo said of Mr. Worster.

Specifically, Mr. Penn alleged Mr. Worster threatened to kill him, which provoked him to shoot.

“We were obviously very pleased with the conclusion (the jury) reached – that’s the conclusion we felt was appropriate all along,” Mr. Krasnoo said.

He also expressed gratitude to the jury for considering seriously the application of “mitigating circumstances” in the case. The jurors, whose deliberations were prematurely cut short Friday when the courthouse lost power, had requested the judge provide further clarification on the meaning of mitigating circumstances, which he did before they restarted deliberations Monday.

According to Judge Ricciardone, if the prosecutors, led by Assistant District Attorney Brett F. Dillon, could not sufficiently prove Mr. Penn was not acting in self-defense, the law would prescribe the defendant be found not guilty. If Mr. Penn used excessive force in defending himself, however, that would warrant a finding of manslaughter, he explained.

Mr. Penn also could have been convicted of manslaughter had the jury instead found he shot Mr. Worster in the heat of passion, Judge Ricciardone said.

In total, the jury met behind closed doors for more than six hours spanning Friday and Monday.

Mr. Dillon had argued during the trial that Mr. Penn was not acting in self-defense when he shot Mr. Worster nearly a minute-and-a-half after the two had a brief fight in the security lobby of the Albion on Jan. 10, 2014. That interval would have provided sufficient cooling-off time for Mr. Penn, who afterward still made the “deliberate and intentional” decision to shoot Mr. Worster, Mr. Dillon said.

Mr. Krasnoo credited Mr. Penn for withstanding those charges in court.

“My client spoke well on the stand and did not yield his position, despite the rather withering cross examination by the Commonwealth,” he said.