Synthetic mushrooms and other drugs played a role in the Christmas Day 2013 death of Flowery Branch man Alan Scott Fyfe, according to testimony Wednesday in Hall County Superior Court.

Alan Fyfe’s brother, Mark Alan Fyfe, 53, of Flowery Branch pleaded guilty to voluntary manslaughter and felony obstruction of an officer.

Mark Fyfe, originally charged with murder, agreed to a negotiated plea deal.

The factors playing into the lesser charge, said Hall County Assistant District Attorney Jennifer Bagwell, included alleged issues with the investigator and the wishes of the Fyfes’ mother.

Investigator David Treadwell was indicted by a federal grand jury on Jan. 28 in connection with allegedly accepting bribes from a suspected drug dealer.

Pressing forward with the case to trial, Bagwell said, added complications to the prosecution’s presentation of evidence.

The mother of the Fyfes also approached the district attorney’s office and was “asking me to not prosecute it as a murder but asking for a reduced charge with less time than the life sentence that goes with a murder charge,” Bagwell said.

Conditions for the plea deal included evaluation and treatment for mental health and substance abuse.

“Somehow, someway, they found some synthetic psilocybin (mushrooms) and synthetic LSD on the Internet and ordered it together. And then over the next several weeks, they enjoyed it together,” said Fyfe’s attorney Jeffrey Sliz.

Sliz added, “My client digested it, and it altered his whole perception of what reality was and what truth was.”

After 9 a.m. on Dec. 25, 2013, dispatch received a 911 hangup call at Mark Fyfe’s home in the 6000 block of River Hill Drive in Flowery Branch.

A neighbor reported seeing Mark Fyfe up on the deck shooting at Alan Fyfe in the backyard. At least 12 shots were fired, with eight hitting Alan Fyfe.

Alan Fyfe’s body was found face up on the ground, unarmed, with a cellphone in his hand, Bagwell said.

Family members “told us that the defendant was upset because the victim was going to take the defendant’s son with him ... to celebrate Christmas,” Bagwell said.

Alan Fyfe, Sliz said, had hidden the rest of the drugs on that morning.

Sliz said Mark Fyfe, under the influence of the hallucinogenic drugs, incorrectly believed his brother was going to kidnap and hurt his son.

Sliz and Mark Fyfe agreed to the terms of the deal.

“It will show him some degree of clemency and mercy,” Sliz said. “It will allow the family to put this behind them without the requirement of having to go through a trial.”

Superior Court Judge Andrew Fuller handed down the maximum 20-year prison sentence for the voluntary manslaughter charge. The felony obstruction of an officer count carried a five-year consecutive sentence with the first two years to be served in confinement.