A Los Angeles man is missing after he disappeared while walking his dog, who returned to his home with human blood on his leash.

Darwin Vela, 22, left his home around 9 a.m. Tuesday to walk his chocolate lab Cocoa, around the time his fiancé, Kelly McLaren, was showering.

“When I came out, I heard the dog crying," McLaren told the Los Angeles Times. “He was outside and alone and Darwin wasn’t there.”

That’s when McLaren said she noticed blood on the dog’s leash and called 911.

"His tail was between his legs and he was hunched over crying,” she told NBC Los Angeles. “"I grabbed the leash and looked down and there was a thumbprint-size spot of blood."

Tests on the blood confirmed that it was human, police said. A search was conducted for Vela on Thursday night, but he wasn’t found.

While police are unsure what’s behind Vela’s disappearance, his fiancé told NBC Los Angeles that the couple are witnesses in a criminal case. A preliminary hearing was held in the case on Thursday.

“We were witnesses to a crime, and we were supposed to testify today,” McLaren told KTLA.

The LAPD said they will be looking into that angle in their investigation of Vela’s disappearance.

"The circumstances caused us concern and caused his family concern, so we are looking into that," LAPD Deputy Chief Kirk Albanese told the station.

Vela’s fiancé said it would be out of character for him to run away, adding that the missing 22-year-old is close to his mother.

"He wouldn't. Even if he could somehow leave me -- which he wouldn't, we're going to get married, we're starting a family -- he would never, ever leave his mother," McLaren told the Times.

Vela was described as a Hispanic male with black hair and brown eyes, 5-feet-6 and weighing about 160 pounds. He was wearing a dark-green beanie, black shirt and blue jeans when he was last seen.

Anyone with information about Vela’s disappearance or his whereabouts is urged to call LAPD detectives at 213-996-1800 or 877-527-3247. Tips can also be submitted anonymously via Crime Stoppers at 800-222-8477 or via text at 274637.