SAN LEANDRO — A former San Leandro police officer has been criminally charged with having unlawful sex with a 17-year-old girl who was part of the department’s Explorer program, authorities said Tuesday.

Marco Becerra, 26, resigned on Oct. 25, less than two weeks after the department opened an investigation, according to a news release from the department Tuesday.

According to court documents, Becerra, in an Oct. 20 interview with investigators, “confessed to being in a sexual relationship with the victim over the past month and a half.”

Because of the incident, the Explorer program has been temporarily suspended while an internal review is conducted but will be fully resumed later, police said.

According to prior media accounts, Becerra was a member of the program when he was a teenager.

Police were notified of the suspected misconduct on Oct. 13 by the Alameda County Social Services Agency and immediately launched criminal and administrative investigations as well as contacting the District Attorney’s Office.

According to court documents, investigators met with the girl, who told them she and Becerra became friends through the Explorer program and corresponded via phone and social media.

According to the documents, the two engaged in sexual intercourse at a location in San Leandro on Sept. 11, Sept. 26 and Oct. 12.

Becerra, a member of San Leandro department for three years, was charged Nov. 8 with three felony counts of unlawful sexual intercourse with a minor.

The department release said Becerra was off-duty when the activity occurred.

The release stated that Becerra “acted independently and this was an isolated incident involving only Mr. Becerra and the 17-year-old victim.”

In the release, Chief of Police Jeff Tudor said, “I am upset and disappointed by the unethical and criminal behavior of one of our officers. These actions are absolutely inconsistent with the ethical standards of the San Leandro Police Department, and we will not tolerate this type of behavior.

“We are deeply concerned for the victim and her family, and we respect their concerns for maintaining privacy in this matter,” Tudor said.

Attorney Michael Rains, who represents Becerra, said the relationship between Becerra and the girl “was consensual” and that they had “strong emotional feelings for one another.” But he said Becerra knows that it was wrong to have a sexual relationship with the girl, whose parents he had met.

Rains said Becerra also “feels ashamed and sorry” for bringing disrepute to the San Leandro department and that he realizes his conduct may have cost him his career in law enforcement.