Genaro Olaguez, 53, had been living at a relative's California home before his arrest Tuesday, Deputy US Marshal Frank Newsom said yesterday.
Olaguez is suspected of killing a commissioner and seven other city officials in Sinaloa, Mexico, in May 2000. Four others also were seriously wounded.
The marshals service has been given few details on the killings, Newsom said. "All I know is heavy weapons" were used, he said.
Newsom and Sacramento County Sheriff's Sgt Lisa Bowman said Olaguez was deported to Mexico yesterday.
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Authorities learnt Tuesday that Olaguez was living at the residence. They watched the house until they saw Olaguez return.
Ed Shaver, a public defender representing Olaguez, did not immediately return a telephone message.
Robert Himelblau, a spokesman for the San Joaquin County district attorney's office, also did not immediately respond.