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Authorities probing the disappearance of a Hollywood executive and former UCLA basketball player say foul play is being "strongly" considered, with a detective telling FoxNews.com elements in the case "are just not right."

Gavin Smith, a 20th Century Fox movie executive and former UCLA basketball player from West Hills, disappeared May 1 after driving away from a friend's Los Angeles-area home in his black Mercedes-Benz. Certain circumstances surrounding his disappearance "are just not right," a law enforcement source told FoxNews.com Thursday. His family agrees.

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"I know that he would never leave his boys," Smith's sister, Tara Addeo, said of the 57-year-old married father of three. "There’s no way my brother would kill himself."

Smith and his black Mercedes-Benz have not been found, the law enforcement source said, and there has been no activity on his bank accounts. Smith, who was staying with a friend at the time of his disappearance, also left behind personal items at the home -- including a cellphone charger and shaving cream -- leading police to believe he had planned to return at some point.

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No persons of interest or suspects in the case have been named publicly.

"I want to hope that he just got into a real bad place and felt he needed to leave for awhile and clear his head because I don’t want to think of the alternative," Addeo told FoxNews.com.

"He's someone I've looked up to my whole life," she said, noting that she spoke to Smith the night before he disappeared. "It's very difficult. Our family is not complete, and we crave answers."

A detective with the Los Angeles County Sheriff's Department confirmed Thursday that the West Hills home of John and Chandrika Creech was searched in June in connection with Smith's disappearance.

John Creech, an admitted drug dealer, is now in police custody for an "unrelated matter," and has not been named a person of interest in the Smith case "at this point," the source said. He and his wife have retained a lawyer.

Creech, 39, was arrested by Glendale police in 2010 for making a drug drop and pleaded guilty, according to local reports. At a court appearance in June, he was remanded into custody by the judge. His sentencing hearing, which was set to happen last week, has been rescheduled for Aug. 29.

Authorities, including homicide detectives and a SWAT team, seized boxes, a computer and a black SUV belonging to John Creech during their raid of the home, Fox affiliate KTTV reported.

Another source close to the case told The Los Angeles Times that Smith was having an affair with Chandrika Creech. One of Smith's family members told FoxNews.com that he met Chandrika Creech while the two were in a drug rehabilitation program four years ago.

Addeo said Smith's cell phone gave off its last signal that same night in Sylmar, about 30 minutes from the West Hills home we he had been staying.

Smith's wife and children have remained largely silent in the case, except for occasional tweets from Smith's oldest son, Evan, a forward for the USC men's basketball team.

Smith worked in the movie industry for 18 years and helped distribute blockbuster hits such as "Avatar" and the "Star Wars" trilogy. The executive, who is 6 feet, 6 inches tall, was also a member of UCLA's 1975 national championship men's basketball team.

A $20,000 reward is being offered for any tips leading to Smith. Anyone with information on the case is being urged to call the Los Angeles County Sheriff's Department at 323-890-5500.