Congressman Joe Garcia’s chief of staff abruptly resigned Friday after being implicated in a sophisticated scheme to manipulate last year’s primary elections by submitting hundreds of fraudulent absentee-ballot requests.

Friday afternoon, Garcia said he had asked Jeffrey Garcia, no relation, for his resignation after the chief of staff — also the congressman’s top political strategist — took responsibility for the plot. Hours earlier, law enforcement investigators raided the homes of another of Joe Garcia’s employees and a former campaign aide in connection with an ongoing criminal investigation into the matter.

“I’m shocked and disappointed about this,” Garcia, who said he was unaware of the scheme, told The Miami Herald. “This is something that hit me from left field. Until today, I had no earthly idea this was going on.”

Jeffrey Garcia, 40, declined to comment. He also worked last year on the campaign of Democrat Patrick Murphy of Jupiter, who unseated tea-party Republican congressman Allen West. Murphy has not been implicated in the phantom-requests operation.

The Miami-Dade state attorney’s office, seeking electronic equipment such as computers, served search warrants Friday at the homes of Giancarlo Sopo, 30, Joe Garcia’s communications director; and John Estes, 26, his 2012 campaign manager. Neither Estes nor Sopo responded to requests for comment.

A third search warrant was also executed, though it wasn’t clear where.

Joe Garcia said he would likely put Sopo on administrative leave for the time being.

The raids marked a sign of significant progress in the probe that prosecutors reopened in February, after a Herald investigation found that hundreds of 2,552 fraudulent requests for the Aug. 14 primaries originated from Internet Protocol addresses in Miami. The bulk of the requests were masked by foreign IP addresses.

It is unclear if the requests from domestic and foreign IP addresses are related to the same operatives.

The Miami Herald found that the ballot requests were clustered and targeted Democratic voters in Garcia’s congressional district and Republican voters in two Florida House of Representatives districts, indicating a concerted effort by a mystery computer hacker or hackers.

Only voters, their immediate family members or their legal guardians can submit requests for absentee ballots under state election laws. Violations may be considered third-degree felony fraud. Using someone’s personal information — as required in online ballot-request forms — may also be considered a more serious, first-degree felony.

None of the identified requests were filled because the elections department’s software flagged them as suspicious. But had they slid by, campaigns would have been able to direct phone calls, fliers and home visits to the voters to try to win their support — if not attempt to steal the ballots from unsuspecting voters’ mailboxes.

Miami-Dade State Attorney Katherine Fernández Rundle said her office has targeted absentee voting, which she considers problematic, both through the criminal investigation and “active advocacy’’ seeking to change laws in Tallahassee and at County Hall.

“Historically, absentee voting is the source of all voter fraud,” she said in an interview, crediting The Miami Herald for its investigation.