Mangasaryan faces a maximum sentence of 50 years to life.
His accomplice and alleged getaway driver, 20-year-old Glendale resident Arpiar Terrgalstanyan, was found guilty of second-degree murder, Dávila-Morales said.
Terrgalstanyan was also found guilty on a weapons possession charge.
Terrgalstanyan faces at least 15 years to life in prison for the charges, Dávila-Morales said.
Expert witnesses, friends and family testified during the more than two-week trial at the Los Angeles County Superior Courthouse in Pasadena.
Voskanian had reportedly owed Bella Stepanyan, 26, of Burbank, a large amount of money. Authorities said the men were acting on her behalf.
Stepanyan was later arrested and convicted of being an accessory after the fact.
Prosecutor Russell Moore argued cell phone records showed that Terrgalstanyan and Mangasaryan were in the vicinity of Voskanian's home on the 4200 block of Jacaranda Avenue during the time of her murder. The records, he said, also proved they were working together to kill her.
Ammunition matching the same caliber used to kill Voskanian was also found in Terrgalstanyan's car, authorities said.
Attorneys for the men, Donald Levinson and Michael Levin, claimed that the prosecution's case was based on circumstantial evidence, including gunshot residue testing and suspect descriptions.
Calls made to each lawyer were not returned by Thursday afternoon.
The men are scheduled to be sentenced Sept. 29.