The eight-woman, four-man jury convicted Cameron Matthew Parker, 29, after deliberating eight hours over two days.
San Diego Superior Court Judge Ken So set sentencing for March 9. Parker, who showed no reaction to the verdict, remains in jail without bail.
Deputy District Attorney Melissa Vasel said Parker faces a sentence of 26 years to life in prison. First-degree murder carries 25 years to life and Parker faces an extra year as the jury determined he personally used a knife in a homicide.
Parker’s attorney, Roland Haddad, afterwards declined comment about the verdict.
A co-defendant, Samantha Grace Passmore, 24, pleaded guilty to voluntary manslaughter and was sentenced Jan. 11 to seven years in prison.
Passmore was ordered to pay for $2,741 in costs of the funeral for Tuttle, 40, who died a week after he was injured by Parker on April 14, 2017, at the San Diego Motel on Mission Bay Drive.
Passmore received credits for 301 days in jail and was fined $2,324 by Judge Michael Groch.
Tuttle formerly owned a bike store in Pacific Beach and was also an artist.
A security camera at the San Diego Motel at 4780 Mission Bay Drive caught a glimpse of Passmore looking into Tuttle’s motel room before turning away, according to testimony at a preliminary hearing.
It was believed at that moment Parker was fighting and stabbing Tuttle on April 14. He was hospitalized at Scripps La Jolla, but died there on April 21 from blunt force trauma injuries.
A pathologist testified Tuttle had four rib fractures and stab wounds. He died of blunt force trauma.
A police officer testified Tuttle told him in the hospital that it was possible his attacker, whom he did not know, was the jealous boyfriend of a woman he knew.
Tuttle said his attacker threw a microwave oven at him, striking his head, the officer said.
Parker and Passmore were arrested for murder on April 25 where they were staying at a Mission Valley motel.
The trial began Jan. 16 in the old central courthouse and ended in the new courthouse at 1100 Union St.