Dunwoody police Detective Jesus Maldonado took the stand Monday morning and told a judge why a 15-year-old girl was stabbed 53 times by her brother: She took too long in the bathroom.

Moldonado testified that Gavin Henderson, 27, had moved in Lacota Apartments with his mother, Rochelle, and his siblings after he got out of a Florida prison last year. He’d done several years for violent crimes, records show, and had nowhere else to go.

But the family found Henderson ornery. Once, Maldonado testified, he pulled a knife on another of his sisters. But no one called the police. The family diffused the situation privately.

Then came June 18.

Around 3 p.m., Henderson needed to use the bathroom, but his sister, Keaira Henderson, a 15-year-old Alpharetta High student, was in it.

Henderson, bloodied by the violence, walked to a nearby store, the detective said.

He allegedly placed the knife on the counter and asked the clerk to call 911. He told her there had been an “accident,” gesturing to the wet crimson on his hands and T-shirt.

Police arrived and arrested him, soon filing murder charges. When officers looked over Keaira’s body, they couldn’t count how many times she’d been stabbed, except that it was far too many to survive. The medical examiner’s office came up with 53.

In the days after, friends and family lamented the girl, who had wanted to be a lawyer and was liked enough at her school that friends gathered on the football field to remember her.

There was no family in the courtroom to hear all this, though they would likely know much of it already because it played out in front of the 12-year-old.

Henderson, whose attorney made no argument on his behalf, sat stoically in court.

When the judge said there was enough evidence for the state to continue its prosecution, Henderson rose and went with deputies back to his cell, the place he’d known he was going from the first thrust of the knife.