PORTLAND, Ore. -- Portland police arrested the fifth teenage robbery suspect Thursday in a racially tinged attack at an Interstate MAX platform.

Investigators said a 28-year-old woman was at the Prescott Street stop Monday evening when she saw a group of teens harassing an older passenger. When she stepped in to confront them the suspects they called the victim, who is white, with what police referred to as “racially derogatory” names.

Then they beat the victim and stole her purse, according to police.

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Three 15-year-olds and a 14-year-old were arrested for assault and robbery in the attack. By Thursday, charges were dropped against one of the suspects, another made a plea deal. The 15-year-old suspects will be charged as adults under Measure 11 guidelines.

Officers arrested the 14-year-old boy after a woman said her son was robbed at a bus stop at gunpoint the day after the MAX attack. That information, combined with surveillance video of the Monday evening attack, led detectives to the boy. No weapon from the robbery has been found, police said.

He will be charged with robbery and intimidation.

The victim's brother told KGW Thursday that she suffered cuts and bruises, and was going back to the hospital to check for a possible concussion from a full beer can thrown at her.

She wished to protect her identity for fear of retaliation, her brother Jordan said.

"It gets to be summer, we see this happening a lot with groups of young people, see more and more of this street thuggish behavior," Portland Police Sergeant Brian Schmautz said.

 "It has to do with groups of people feel empowered because they're in a group, and they get more of this gang or group mentality, where they feel like they're invincible."

Last week, four teens were arrested for assault and robbery after passengers said they started demanding money and other items on the Yellow Line train, then punched some passengers.

TriMet does have officers riding the trains on the Yellow Line. And police say the problem is communitywide -- not just on the trains.

"It is more sad that as people were watching this no one even called 9-1-1," Jordan said. "It'sabsolutely terrifying that other people could be going through the same thing and nothing happens."

 Also: Teen pleads guilty in Gresham MAX attack