Des Moines police are looking for up to 20 young men accused of attacking a couple in the downtown skywalk.

Police tell station KCCI it all happened when a 19-year-old woman and 21-year-old man walked past a group of teens outside the Wellmark YMCA.

"They came across the group of teens who kind of just seemed to be hanging out, but something didn't look quite right,” Des Moines police Sgt. Paul Parizek told KCCI. “(The woman) simply asked them, ‘Is everything okay guys?’ and they responded in a violent fashion."

A witness he yelled 'call the police' hoping that would stop the attack and said the group pinned the 21-year-old against the glass of the YMCA.

Police say crime in the Des Moines skywalk is very rare, but the head of a security group that patrols that area says conditions are becoming so dangerous, he may pull his officers out of there. The head of the Conly Group says they've lost almost 100 hours of time due to injuries.

Authorities are investigating and hope to soon file charges.

to read the full story from KCCI.