Luchko, seen as a fiercely loyal employee of the powerful Philadelphia Democrat, had been expected to tell jurors that Fumo ordered him to destroy years worth of e-mails because of an FBI probe.
The 65-year-old former lawmaker sat expressionless at the defense table as prosecutors said they only learned of Luchko's continued contact with Fumo on Friday.
Fumo is charged with misusing more than $3.5 million from the state Senate, a South Philadelphia charity and a museum. He has pleaded not guilty.
Defense lawyer Dennis Cogan said he was in the dark about the correspondence until getting the news Saturday from prosecutors. Both sides told the judge they needed time to examine the new evidence and reassess their trial strategies. U.S. District Judge Ronald L. Buckwalter told lawyers to return to court Tuesday afternoon.
The Luchko e-mails and blog posts number in the thousands of pages, Assistant U.S. Attorney Robert Zauzmer said. He did not specify how frequently Luchko was e-mailing the senator, whose 139-count corruption trial began in mid-October.
"It's a very, very voluminous set of documents," Zauzmer said.
It was not immediately clear how the government learned of the e-mails, but prosecutors said Luchko was messaging Fumo up to and during the trial.
Luchko, 52, of Collingdale, awaits sentencing after pleading guilty in August to 29 felonies in the Fumo case - one count of conspiracy and 28 counts of obstruction. He was expected to testify for a full day or more against his former boss.
His lawyer, James C. Schwartzman, did not immediately return a phone message left at his office Monday morning. A home number listed for Luchko has been disconnected.
The new e-mails may contradict earlier evidence in the case and impeach Luchko's credibility, Cogan said.
"He's a serial e-mailer," Cogan said of Luchko. "If he has a thought, he puts it in an e-mail."
Fumo is accused of using the staff and assets of the Senate, charity and museum to do his personal and political work. Evidence against him includes e-mails written by Luchko in which the Senate technician voiced frustration - but also devotion - regarding his round-the-clock responsibilities for Fumo.
Luchko complained that his chores included driving people to get their hair done, wrapping 150 Fumo bobblehead dolls and wiring a yacht for Internet access.
Yet, he wrote, "I love my job and wouldn't trade it for any job in the Senate!"
A year later, he wrote in an e-mail recovered by authorities that the "Boss is driving us ALL nuts with this FBI madness."
Prosecutors, who are nearing the end of their case, said they may decide not to call Luchko. They could get some, but not all, of his likely testimony from Mark Eister, another computer technician who also pleaded guilty in the case.
The government has only a few witnesses left to call, including Eister and the lead FBI agent on the case. The defense was expected to begin its case as early as next week.
Fumo left the Senate in 2008 after 30 years in office. Over the years, he came to control 90 Senate jobs before the charges led him to resign as the ranking Democrat on the Senate Appropriations Committee. He controlled more jobs through his seats on various corporate and civic boards.
A multimillionaire banker and lawyer, Fumo beat two previous indictments early in his political career. In 1973, authorities dropped vote-fraud charges against him, while a 1980 conviction for his role in an alleged ghost-worker scheme was eventually overturned.
