Deputy District Attorney Jeffrey Dort said Brian Eleron Hancock, 49, will have to serve a minimum of 25 years in prison before he could become eligible for parole.
Dort said Hancock, of National City, faces a sentence of 85 years to life in part because of his prior convictions for arson in 1999 and residential burglary in 2003.
"I'm totally satisfied," said the victim's brother, Kirk Bentz, after the verdict. "This is the correct and just verdict for Peter."
Bentz, 68, was last seen leaving the 24-Hour Fitness gym on Midway drive on security cameras on Nov. 21, 2017. No credit card or Internet activity has surfaced from Bentz since then. His blood was found in 17 locations in his apartment after investigators looked underneath the carpeting.
Kirk Bentz testified as the trial's first witness and said his brother failed to show up at his home for Thanksgiving after dropping out of sight.
San Diego Superior Court Judge Joan Weber set sentencing for Feb. 26. Hancock remains in jail without bail.
"Brian Hancock brutally killed Peter Bentz," said Dort afterward. "The verdict is appropriate, based on the evidence."
The seven-woman, five-man jury didn't stick around afterward and attorneys did not talk to them. They began deliberations Jan. 22 in a trial that started Jan. 7.
"The San Diego Police Department did an incredible job, piecing together a case no one knew about based on cell phone records and credit card receipts," said Dort, who described it as "an airtight, circumstantial evidence case."
Dort told Bentz's family the defense "went down the slope of 'Let's make Peter as bad as he can be." Dort told jurors Hancock lied on the witness stand.
Jimmy Rodriguez, Hancock's attorney, had argued for acquittal, saying Bentz may be in Mexico and the prosecution had not proved its case. He did not comment afterward.
Hancock, an electrician, denied killing Bentz, whom he described as a sexual partner after meeting him to do electrical work in his Greene Street apartment.
Dort argued to jurors that Hancock wanted revenge for Bentz secretly videotaping him and another woman having sex in Bentz's apartment. A woman testified she had sex with Hancock and thought Bentz might have videotaped it.
The woman testified someone sent her a video that she could not open and she feared it showed her and Hancock. She said Hancock told her he would talk to Bentz about it.
Another woman said Hancock told her he stabbed Bentz seven times. And his wife testified he threw a bag of Bentz's identification and other items off a freeway.
A napkin containing Bentz's blood and Hancock's DNA was found in the bag that was strewn along Interstate 5 near Logan Heights. Hancock was seen on video using Bentz's credit cards and driving his car after he disappeared.
Hancock testified that Bentz told him he was going to Mexico for a vacation and claimed he was in contact with Bentz for five days after he disappeared. He said he had Bentz's permission to use his credit cards and his Toyota Highlander.
Bentz is believed to have buried in Campo because Hancock's phone pinged in a stationary location for 4 1/2 hours in Campo on Nov. 24, 2017. A tag for a tool was found in Campo that Hancock had purchased with Bentz's credit cards, according to testimony.
Angelina Hancock, his wife, testified her husband wanted "to transport Peter's body" in new boxes she had purchased. She testified under a grant of immunity after signing an agreement with the DA's office.
In a conversation Angelina Hancock had with her husband in jail, she said: "he discussed burying Peter." She said she didn't know where he buried the body.
Angelina Hancock testified she first learned of the sexual relationship between her husband and Bentz after reading a sexually-oriented text from Bentz on Hancock's phone while he was in the shower.
"As he recently shared with me about his relationship with Peter, it's something I can't provide for him," said his wife, who has since divorced Hancock after 20 years of marriage.
Hancock's sentence for murder is 25 years, and the judge could add 50 years for the two previous convictions plus 10 years.