Calgary Police have arrested a 30-year-old man in connection with a sex attack on a teenager on Saturday night.

On April 6, at about 5 p.m., a 17-year-old female was downtown in the 400 block of 3 Avenue S.W. when she was approached by a man who convinced her to go with him.

"The victim was on her way downtown to meet with a friend and this man befriended her. As far as I can say, they were strangers to one another," says Acting Staff Sergeant Andy Nguyen.

A short time later, she excused herself to go to a public washroom in an office tower connected to Calgary's Plus 15 system.

The suspect followed her and sexually assaulted her inside the washroom.

The girl fought off her attacker and fled, managing to call for help.

The suspect also fled the scene.

A number of bystanders tried to catch him while others attended to the girl.

The suspect fought his way away when the bystanders caught up to him, and ultimately escaped.

Police attended and managed to track him down using witness information and security camera footage.

He was taken into custody without incident at about 2 a.m. in the southwest community of Wentworth.

Daniel Christopher Mahon, 30. has been charged with sexual assault causing bodily harm, overcoming resistance by choking, and breach of recognizance.

Nguyen says that Mahon is known to police and has been charged before.

Those matters are before the court, Nguyen says, but refuses to comment further on what they may be.

Court documents indicate that Mahon was ordered to stand trial for one count of sexual assault against a female victim.

That incident is alleged to have happened in February 2011.

He was released on bail under strict conditions, including a requirement to report to a probation officer as part of the high risk offender program.

Nguyen says the victim is recovering at home and recieving support. "With the new Child Advocacy Centre that we have, there are resources available, and we're providing support for her."

He took the time to thank the actions of the bystanders in coming to the aid of the girl. "I'd like to thank those witnesses who pursued the suspect and those who stayed to help the distraught victim."

No one else was injured in the attack.

Nguyen adds that while the help was greatly appreciated, the best way to help would be to call 911, provide information, and leave the matter to the police. "It was a good thing what the witnesses did, but I wouldn't recommend that as a normal practice for citizens of Calgary."

Mahon remains in custody and will appear in court on April 11.

Police are reminding residents that if you are going to go meet with somebody that's unknown to you, you should meet in a public area or have a friend along with you to go to if you need help.