A 10-year veteran Los Angeles police officer was arrested Thursday for allegedly having a sexual relationship with a 15-year-old girl who was a member of the LAPD's troubled youth cadet program.

Officer Robert Cain, 31, was arrested around 11 a.m. by Los Angeles Police Department Chief Charlie Beck at the 77th Street Division station, where Cain is assigned.

The arrest is the latest scandal to rock the cadet program, which was shaken last week with the arrest of seven juvenile participants stemming from the theft of three police cruisers.

The 15-year-old girl involved in the alleged sexual relationship with Cain is one of the seven cadets who were arrested, according to the chief.

Beck said the relationship between Cain and the 15-year-old girl appeared to be short-term, occurring "within the past month," but he said investigators were still looking through phone records and social media.

"I believe the cadet has only been with the department for a few months," Beck said. "But the activity that led to the arrest occurred within the past month."

Beck said the relationship appeared to be "consensual," but added that a 15-year-old girl cannot legally give consent. Beck said he made the arrest personally to send a message about the severity of the situation.

"I think it's important to send a message," he said. "Everything I do is calculated to impact either the city of Los Angeles or Los Angeles Police Department.

"I find the actions of Cain, if they are proven, to be despicable. I find them to be absolutely inconsistent with the ethics and standards of the Los Angeles Police Department and they are criminal. And I'm a police officer and I was -- I felt it was my duty to make the arrest."

Investigators learned about the alleged illicit relationship when they reviewed text messages on the arrested teen's cellphone, Beck said.

Mayor Eric Garcetti, who is out of town on vacation and will be attending the U.S. Conference of Mayors meeting in Miami Beach, Florida, starting Friday, said he was disturbed by the arrest.

"There is no higher priority than protecting and guiding our young people, and when they become LAPD cadets, every parent should feel confident that they will be treated with the utmost care every step of the way," Garcetti said in a statement released by his office.

"The charges against this officer are deeply disturbing, and I have been assured he will be prosecuted to the full extent of the law. These allegations represent a total breach of the trust we place in everyone who wears the uniform and a violation of the oath all officers take to protect and serve.

There is an exhaustive review of the cadet program already under way, and I have faith that our program will emerge stronger and justice will be served.''

The Los Angeles Police Protective League, the union that represents LAPD officers, issued a statement saying if the allegations are true, "we applaud the department for taking swift action."

"There should be zero tolerance for any officer who takes advantage of those they are entrusted to protect," according to the union. "We are deeply disturbed by this development and condemn this officer's alleged actions in the strongest possible terms."

On Tuesday, Beck announced the arrests of four additional juvenile cadets, bringing to seven the number who have been nabbed in connection with the theft of a trio of police cruisers, two of which were involved in pursuits that ended in crashes last week.

Three cadets were arrested at the end of the pursuits the night of June 14. Police recovered the two cruisers involved in the chases, then found a third parked nearby.

Of the seven arrested cadets, six were assigned to the 77th Street Division program and one was assigned to Pacific Division. Beck last week suspended the cadet program at those two divisions.

Beck, speaking at a Police Commission meeting Tuesday, said the arrested cadets on a number of occasions impersonated police officers and initiated traffic stops of motorists, although no one who was pulled over was handcuffed, had force used on them or was issued a citation.

The cadet program has more than 2,300 active participants, and Beck continued to express support for the program. He said he still plans to attend the program's graduation ceremony this Saturday, and he encouraged the media and public to attend "so they can see the other 2,200 cadets who so well served this city and are such good examples of young people in Los Angeles."

An LAPD supervisor doing inventory discovered that a squad car was missing from the 77th Street station on June 14, and the investigation quickly identified a female cadet caught on camera driving it off the lot, Beck said last week.

Police spotted two squad cars driving in tandem around 9:35 p.m. that night near the 77th Street station, leading to the chases.

One cruiser crashed in the area of 77th and San Pedro streets, where the driver was taken into custody, police said. The driver of the other stolen cruiser crashed into a vehicle at Adams Boulevard and Central Avenue, and that driver was also was taken into custody.

During one of the pursuits, an officer crashed into a civilian vehicle near the intersection of Gage Avenue and Broadway, but no one was seriously injured.

Investigators believe the cadets used their knowledge of the LAPD's computer inventory system to check the vehicles out under the name of a sergeant who was on vacation, Beck said.

Beck said Thursday it was unclear if the alleged sexual relationship played any part in giving the cadets access to the unauthorized equipment. But Beck said Cain was at one point "in charge of the mechanism by which you check out police equipment" at the 77th Street station.

"I certainly think there may be a connection to the wooing of this underage female and access to the equipment," Beck said. "I don't know. That would be consistent with pedophile-type behavior."

Beck said earlier he "was not sure" how long the cars had been missing, but one of them may have been gone for two weeks.

The LAPD has more than 1,800 black-and-white squad vehicles but they are not all used every day, and because of the suspects' familiarity with the computer system, they were able to conceal the thefts, Beck said.

The vehicles were taken from 77th Street Division Station and the Central Division.

Beck also said last week that the suspects were in possession of some LAPD equipment, including radios and a bullet-proof vest, although no firearms are believed to be missing.

As part of the investigation of Cain, search warrants were served at his Rancho Cucamonga home, on his vehicle, locker, phone and social media accounts, police said.

Cain, who had been assigned to the 77th Street Station for the past two years and was not formally involved in the cadet program, was being held in lieu of $75,000 bail at the Men's Central Jail in downtown Los Angeles, according to sheriff's inmate records that did not indicate a pending court appearance.

Cain was released on bail at 5:17 a.m. Friday morning after posting $75,000 bond, according to LASD records. His court date has been set for July 21.