Police changed the missing person's case to a homicide investigation, making the announcement on Thursday. His wife is trying to stay strong during this difficult time.
"Gavin's just larger than life and charming and funny and sweet and the love of my life, and a really super good daddy and playful with the kids and we just had a good time," said Lisa Smith.
Lisa Smith and her sons have been searching for Gavin Smith since last May, when he didn't pick up his son from school.
"For both of them to disappear, the car and my husband, off the face of the earth, nothing good can come of that," Lisa Smith said.
That car, along with what investigators call "witness statements," turned out to be the key to cracking the case - at least partially.
The vehicle was found in a Simi Valley storage facility in February, and investigators say its "condition" led them to believe Gavin Smith was murdered.
"We were encouraged that the investigation is going forward and that there's some action, and it's of course devastating to hear it out loud, but about time," Lisa Smith said.
Investigators are now looking at a man named John Creech, who is in jail on an unrelated drug conviction, as a person of interest. Authorities say Creech's wife had a relationship with Gavin Smith.
"It's just the worst time of our lives so far, and it's been a long haul getting here," Lisa Smith said.
Gavin Smith's body has not been found, despite dozens of search warrants and law enforcement interviews.
For a family now processing the loss, it can sometimes be too much.
"We love him and we miss him, and we wish it hadn't gone this way," Lisa Smith said.
Detectives believe whoever murdered Gavin Smith was not acting alone and they're still asking for the public's help, especially if anyone saw Smith's black 2000 Mercedes-Benz 420E on or around May 8 or 9, 2012.
If you have information that can help investigators, you're urged to call the Los Angeles County Sheriff's Department Homicide Bureau at (323) 890-5500.