A software programmer testified Monday he had nothing to do with the disappearance of his estranged wife, who hasn't been seen since dropping the couple's two children off at his house a year and half ago.

Hans Reiser, known in programming services as the creator of the ReiserFS computer file system, is charged with killing his wife, whose body has not been found.

Reiser, 44, testified that he has tried to figure out what may have happened to his wife since she was last seen Sept. 3, 2006; the defense has suggested Nina Reiser could still be alive and living in her native Russia.

But prosecutors say she was not the sort of person who would abandon her children. They say DNA and other evidence points to Hans Reiser. His car was found with the passenger seat missing and the floorboard soaked with water.

Recalling the day she was last seen, Reiser said he talked to his wife for about an hour, discussing their children and their divorce. He said he "put a lot of pressure" on Nina Reiser, including accusing her of embezzlement and perjury.

Reiser, who resumed testimony Monday following a weeklong hiatus in the trial, said that he did not hear that Nina Reiser was missing until the evening of Sept. 5, when a friend of hers called to say that she had the children and Nina Reiser had been missing since Sept. 3.

"This just didn't add up," Reiser said.

He said the friend put a police officer on the phone to talk to him. But Reiser said he thought "something strange was going on," and referred the officer to his divorce lawyer.

A few days later, the children were taken into protective custody, Reiser said.

Reiser testified earlier that he took the seat out to make it more comfortable to sleep in the car. He said he bought the books because he realized he was under suspicion and wanted to read up on the topic.