Robert Lee Williams Jr. was in what prosecutors called his "hunting ground" when police arrested him across the street from Irving High School.

A Dallas County jury convicted the 24-year-old Wednesday of sexually assaulting a teacher there as she left school. DNA evidence links him to that case, as well as the rape of a custodian at a nearby school and the attack of an elementary school teacher jogging in the neighborhood.

A jury of nine men and three women could send Williams to prison for life for aggravated sexual assault. Williams has not been tried for the other two attacks that prompted testimony during the punishment phase of his trial.

None of the women are being identified because The Dallas Morning News typically does not identify victims of sex crimes.

Williams has a long history of illegal contact with the school.

Police gave him a trespassing warning and a ticket for being on campus in 2001. In 2003, Williams was arrested when he fought with officers after refusing to leave a basketball game there.

That was the same year he pleaded guilty to stealing laptops from the school.

The first assault, for which Williams was convicted Wednesday, occurred at Irving High School in September 2001. A teacher was getting into her van just before midnight on a parent-teacher night when a man grabbed her from behind.

"Don't scream or I'll break your [expletive] neck," she testified that the man told her. "I believed him."

Then, in October 2001, prosecutors say, Williams sexually assaulted a custodian working at the Irving school district's Union Bower Center for Learning.

That woman testified during the punishment phase of Williams' trial that a man repeatedly slammed her against the wall before dragging her outside to a wooded area. He threatened to kill her if she didn't stop screaming.

"When he finished, he just said, 'Close your eyes and count to 10,' " she testified. "I felt sick. I felt so sick."

She counted to 10, opened her eyes and walked back into the school to call police.

After the woman testified, she walked by the first victim on her way out of the courtroom.

"You did good," the first woman whispered.

The next attack came in January 2003 as an Irving elementary school teacher ran her daily five miles before school. She testified in court that after she finished the first mile, she heard someone coming toward her. She turned and saw a man in a hooded shirt.

"Come on [expletive] [expletive], let's go," she testified he said as he yanked on her arm and picked her up.

They fell and rolled down an embankment. The man landed on top of her. When he put his hand in her mouth to make her stop screaming, the woman testified, she bit his hand hard, "like a dog gnawing on a bone."

Then, the man repeatedly slammed her against the ground and punched her face. He hit her so hard that the woman said she could not see out of her left eye.

Then the man ran away. He left blood from his hand on the woman's shirt.

During treatment for her injuries, which included doctors putting a plate under her eye, the woman found out she had cancer. She is now cancer free.

Williams was arrested in 2005 when DNA connected him to all three attacks.

During closing arguments in the trial's guilt-innocence phase, Williams' attorney, Richard Franklin, argued that the work in the case was "sloppy." He cited a typo in a number on a chart showing a DNA match from one of the attacks to Williams.

"You can't let them get away with this sloppy stuff, and this sloppy stuff convicts him or it sets him free," Franklin told jurors.

Dewey Mitchell, the prosecutor, said the defense was twisting reality. The raw data used to create the show-and-tell chart for the jury have the correct numbers, he said.

"Mr. Franklin had the right to question our evidence," he said. "He doesn't have the right to stand in front of you and make things up" by insinuating the DNA match was flawed.

Testimony in the case resumes Thursday.