Laura Sodi, a Mexican actress and singer known by her stage name Laura Zapata, is seen in this photo from late 2001 in Mexico City. (AP Photo)

MEXICO CITY (AP) -- Laura Zapata, sister-in-law to Sony Music Chairman Tommy Mottola, has been released after kidnappers held her for 18 days, Mexico City's attorney general said Friday.

Bernardo Batiz said authorities did not know the whereabouts of Thalia's other sister, Ernestina Sodi, who was kidnapped along with Zapata on Sept. 22. Laura and Ernestine are the sisters of the Latin Grammy performer Thalia.

"The chief of police has told me that (Laura) showed up" Thursday, Batiz told reporters at a news conference. He said he had no other details of Zapata's release.

Thalia was in Mexico after the kidnappings, but refused to talk to police or the media.

Zapata's family had declined to file an official report on the disappearance of the two sisters, and had asked police to stay out of negotiations.

Police found Zapata's car abandoned on a Mexico City road after the two sisters left a play in which Zapata had a starring role. Media reports quoted unidentified witnesses as saying the two were followed and ambushed at a stop light, but police would not confirm the reports.

Shanik Berman, a journalist and friend of Zapata's, had said kidnappers demanded a ransom of $1 million for the release of the two sisters. It was unclear if the ransom was ever paid.

Kidnappings are common in Mexico but many go unreported, partly because family members fear police may be involved or the victim could be killed during a botched rescue attempt.