It was the most mundane of household problems, jurors were told Monday, that prompted a fight that ended in death.

“This started when a bathroom toilet was clogged,” Jennifer Dayton said from the well of a Montgomery County courtroom, “and it went downhill very fast.”

Her client, James Biddinger, 27, is accused of murder in the May 2011 stabbing death of Kevin A. Mbayo, 22. The trial started late Monday afternoon and is expected to last at least a week.

These details appear to be undisputed:

Biddinger lived in a Germantown townhouse with several other rent-paying occupants. Mbayo often would spend the night on a sofa, but he did not pay rent. This had begun to irk Biddinger.

James Biddinger (Courtesy Montgomery County Police )

The evening of May 3, Biddinger went to the Hard Times Cafe with at least two friends and had a couple of drinks. They came back to the townhouse.

Mbayo was already there. He and Biddinger had a confrontation and Mbayo was stabbed.

Dayton, an assistant public defender, says her client acted in self-defense.

“Self-preservation is an instinct of every human being,” Dayton said.

But Assistant State’s Attorney Vlatka Tomazic says that Biddinger made conscious decisions before plunging a stiletto into Mbayo’s back. After the stabbing, Biddinger fled the scene, she said, by catching a ride to a Wal-Mart parking lot and discarding the knife along the way.

“What did he do with the knife?” Tomazic said to jurors. “He threw it out the window.”

At some point, Biddinger also called 911, she said, but he blamed the confrontation on Mbayo.

Dayton offered additional details on what precipitated the stabbing. She said that a friend of Biddinger’s wanted to use an upstairs bathroom but told Biddinger there was no toilet paper. Biddinger went to a ground-floor bathroom to try to find some.

“He was met with the overwhelming odor of human feces,” Dayton said.

And he did not find toilet paper.

Whatever was said, “Kevin Mbayo didn’t take kindly to it,” Dayton told the jurors.

She said that evidence will paint the picture of a violent fight, one that ended in a tragedy. “Mr. Biddinger is innocent of murder,” she said.