Lawyers for Donald L. Blankenship, the former coal executive accused of conspiring to violate federal safety standards before 29 people were killed at the Upper Big Branch mine in West Virginia, rested their case on Monday without calling any witnesses.

The defense’s strategy, which emerged Monday morning in Federal District Court in Charleston, surprised many legal experts who had been monitoring the proceedings. Mr. Blankenship’s lawyers had been expected to summon witness after witness in their effort to undercut the case, which jurors have heard for more than a month. Closing arguments are expected to begin Tuesday.

“It’s clear that the defense team thinks that they inflicted enough body blows in the government’s case to justify resting now,” said Michael B. Hissam, a former federal prosecutor who worked on the Upper Big Branch investigation and now, as a lawyer in private practice, represents coal-industry clients. “This is an unusual strategy, though. The general rule of thumb is that if you feel strongly about your defense, you put your defense case on.”

Mr. Hissam, who has attended much of the trial, said Mr. Blankenship’s lawyers had signaled that they would present a deep, wide-ranging defense. One prospective witness, he said, was waiting outside the courtroom.