San Diego, California (CNN) -- An investigation into the death of two brothers and the fiancee of one is focusing on an unidentified man seen in the San Diego shopping mall where one victim left work shortly before she was fatally wounded, police said Friday.
San Diego police made the announcement one day after authorities identified a decomposed body found in a car trunk 100 miles away in Riverside as being that of Gianni Belvedere, 24.
He was the fiance of Ilona Flint and the brother of Salvatore Belvedere, both 22, who were found shot December 24 in Salvatore Belvedere's car.
What some first speculated as a love triangle gone wrong with two brothers is now a triple murder mystery.
"We have much work to do and there are many detectives working on this case," homicide Lt. Mike Hastings told reporters.
San Diego authorities, now leading the investigation, declined to comment in detail about the Gianni Belvedere's autopsy other than to say the manner of death was a homicide, and the final autopsy report won't be available for a few weeks, said Hastings.
A series of events began at 1:15 a.m. on Christmas Eve Day when Flint called 911 to report she had been shot. She had just finished working at a Macy's in the mall, which was keeping late hours for holiday shoppers, and her future brother-in-law picked her up in the middle of the night.
Police found her dead in car with a gunshot wound to the head, and Salvatore Belvedere was in the driver's seat fighting for his life with gunshot wounds to the head and torso. He died three days later.
Police searched for Gianni Belvedere, 24, who was listed as missing. Last Friday, police in Riverside found the decomposing body of a young man in the trunk of a car parked in a fast-food restaurant. The body was that of Gianni Belvedere.
The "person of interest" sought by police was seen in the mall at 11:15 p.m. on December 23 and again at 12:15 a.m. on December 24, Hastings said.
He was described as a man of unknown race, 5-foot-10 to 6-foot tall, wearing a black hoodie with unique white bands around the sleeves near the biceps, dressed in tan pants and all-white tennis shoes, Hastings said. He did not explain the source of that description.
A Belvedere family reward of $10,000, initially offered for the location of the missing brother, is now being offered for information leading to the arrest and conviction in the case, Hastings said.
The two brothers worked at a family Italian restaurant in Lakeside, outside of San Diego, a friend said. Flint and the two brothers lived in the Belvedere family home in San Diego, said friend Andre Briones.
The engaged couple were together for about seven years and met in Provo, Utah, where Flint's family lives. Flint then moved to San Diego at her fiance's invitation, Briones said.
CNN's Chuck Johnston and Casey Wian contributed to this report from San Diego. Michael Martinez wrote and reported from Los Angeles.