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IRVING (CBS 11 NEWS) – Irving police arrested a man for stabbing a woman with a screwdriver, as she was on a treadmill at the gym Tuesday morning.

Phillip Roberts, 32, is charged with aggravated assault with a deadly weapon.

Phillip Roberts, 32, charged with stabbing a woman at an Irving gym. (credit: Irving Police)

Phillip Roberts, 32, charged with stabbing a woman at an Irving gym. (credit: Irving Police)

The attack happened just before 6 a.m. at the 24 Hour Fitness on West Airport Freeway.

Witnesses say Roberts approached the woman from behind, and pulled her off the treadmill, then began stabbing her in the back with a screwdriver.

Three men separated Roberts and pinned him down until officers got there. Police say the 49-year-old woman was stabbed at least three times, and was taken to Parkland hospital for treatment.

Police say the woman did not know Roberts at all; the motive is unclear.

Justin Harper was running on a nearby treadmill at the time.

“You’re at a gym and you think you’re in a safe place and you don’t know,” Harper said.

(credit: CBS 11 News)

(credit: CBS 11 News)

Harper is a reserve police officer for Blue Mound. He works out regularly at the 24 Hour Fitness because it is close to his teaching job, at Singley Academy in Irving ISD.

Harper jumped in when he saw what was happening.

“I had the front part of his body and the other guy had his back. I put his arms behind his back because I saw something in hand,” said Harper.

Irving police say Roberts has a membership at 24 Hour Fitness – something the company will not confirm.

But employees at the Irving gym say Roberts has been at the facility before.

“I know I’ve seen this guy. I don’t know if he’s a vagrant or a homeless person, but I know I’ve seen him outside,” said Harper.

Irving police say someone else working out this morning thought Roberts looked suspicious. He was not wearing gym clothes, and was carrying a suitcase. That gym member called 911, but the responding officers left after police say the gym staff told them Roberts was not causing any trouble.

In a statement, a spokesperson for 24 Hour Fitness said the club routinely assesses security needs, and added that safety is a top priority.

“It is kind of scary where, that could have been me on that treadmill. If something snapped in his head, that could have been anybody in that gym,” said Harper.

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Jennifer Lindgren