By Matt Petrillo

PHILADELPHIA (CBS) — SEPTA Police have released photos of the suspects wanted in an attack on a SEPTA employee last week. The dramatic video of the worker being attacked at a Center City station has the transit workers’ union calling for the SEPTA police chief to resign.

The brutal beating happened Monday night at the 15th and Market Station.

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Officials say a SEPTA worker is recovering after that brutal attack. Security video released by SEPTA’s transit union, Local 234, shows two people in hoodies punching a SEPTA worker before he’s knocked to the ground. A group of others then swarm around the 55-year-old victim to join in on the attack.

“When I saw it, I was horrified,” Local 234 President Willie Brown said.

SEPTA transit union officials say the unprovoked attack happened around 11 p.m. Monday at SEPTA’s 15th Station under City Hall. Union workers say they’re not safe and they are again calling for SEPTA’s police chief to resign.

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“I think he’s in over his head, he’s not showing great leadership, he’s not giving us any plan to show this is what we’re doing to secure this station or to make your members safe,” Brown said.

The union initially demanded the chief to step up or step down Monday. That’s when SEPTA announced it would be closing a subway station in Kensington due to maintenance. SEPTA’s transit workers’ union said at the time the real reason was that it’s become too dangerous.

Regardless, SEPTA’s top cop insists he’s the right person for the job.

“I will not be resigning,” SEPTA Police Chief Thomas Nestel said.

At a news conference Thursday, Nestel pointed out he’s working to improve safety.

“Over the past month, discussions have been ongoing about contracting with a security guard firm to put guards on some platforms to maintain visibility,” Nestel said.

The union also says there are just are not enough SEPTA police officers to protect workers and riders.

But SEPTA’s police chief said Thursday his department is at its highest staffing level in the last nine years that he’s been chief.

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A $1,000 reward is being offered for information leading to the arrests of four suspects.