The tiny jail on Catalina Island is hardly Alcatraz. Just ask Frank Carrillo.

The pro golfer turned jewel thief couldn’t believe his luck when he was moved out of his bleak Men’s Central Jail cell in downtown L.A. and allowed to do his time on the sunny tourist isle.

But things got even cushier when he met a Los Angeles County sheriff’s captain interested in shaving a few strokes off his golf game.

Carrillo said Capt. Jeff Donahue escorted him in a patrol Jeep to a hilltop golf course last summer. There, dressed in his yellow inmate jumpsuit, Carrillo said, he gave the captain pointers on how to improve his swing and reduce a double-digit handicap.

Word of the free lesson, however, ended up being costly for Donahue, who is under investigation for an inappropriate relationship with an inmate. The allegations were detailed in a complaint by one of Donahue’s subordinates.

Carrillo, who compared his time in jail for multiple felonies to “hitting the lotto,” thought Donahue should be emulated, not investigated.

“He was amazing to me,” said Carrillo, who believes the captain benefited from his lesson.

“He kind of has this swing that’s old school and risky, but he hits it every time,” Carrillo said in a phone interview. “I would probably say he’s a 14 or 15 handicap. Not too bad.”

Donahue, now on medical leave, headed up the sheriff’s Avalon force, which polices Catalina and San Clemente islands and the ocean waters separating them from the mainland. The sheriff’s station in Avalon has its own lockup and trusties — well-behaving inmates who get a little extra leeway in exchange for taking care of chores at the site.

Carrillo ended up as a trusty at the island jail after making headlines for stealing a World Series championship ring from a former Dodger at a charity golf event. He eventually pleaded guilty to charges related to a string of golf course thefts involving cash, Rolex watches and other jewelry valued in the tens of thousands of dollars. He was sentenced to two years and has since been released.

The way Carrillo, 41, tells it, his charm, otherwise clean record and good behavior earned him the transfer to Catalina. “It was like camp,” he recalled.

Carrillo said word of his history as a pro golfer in Canada quickly got around among station deputies. After developing a rapport with Donahue, he said, he broached the idea of leaving the station with the captain to play some golf.

“I knew it was a crazy thing to say,” Carrillo recalled. “But the first thing he said was, ‘Maybe I need a few pointers.’ ”

A deputy at the station who filed the claim complaining about the incident said Carrillo was allowed to change into slacks and a polo shirt for the outing. Carrillo recalled staying dressed in his “county yellows” when the two took the short drive to the course, where they hit balls. “They don’t really have a driving range. It’s a net,” he said.

Shortly after the lesson, Carrillo said, Donahue took a golfing trip to Palm Springs. When he returned, he said, the captain raved about how much his swing had improved.

Sheriff’s officials are strictly forbidden from fraternizing with inmates. Excursions off site are rarely granted and require special security clearances when they are.

Deputy William Cordero, who filed the claim, said Donahue documented in the jail log that Carrillo never left the station.

The allegations caused a rift at the station, Cordero said. Some deputies had no problem with their boss’ actions, but some thought his conduct was illegal, according to the deputy’s filing. Cordero said he spoke out about the incident and was harassed by other deputies as a result. He has since been transferred off the island.

In his filing, Cordero also alleges that Donahue told him the golf outing was subsequently cleared by Sheriff Lee Baca, who was on the island in July for a charity event. Carrillo confirmed that account, saying Baca knew him from charity golf tournaments in the past and spoke to him during a tour of the station. The outing came up, Carrillo said, and Baca seemed to approve, characterizing the excursion as “rec time.”

Baca’s spokesman Steve Whitmore denied Carrillo’s recollection.

“They may have said hello, a conversation may have occurred, but Baca never condoned this guy going out and playing golf,” Whitmore said. “He would never do that. He would never condone taking a trusty out and having them go play golf.”

robert.faturechi@latimes.com

Times staff writer Andrew Blankstein contributed to this report.