The man accused of killing two people on light rail had been stopped eight times by TriMet enforcement and banned from the system for a month in 2015, records show.

But despite hundreds of dollars in unpaid fare evasion fines, nothing kept Jeremy Christian from boarding the Green Line train May 26.

Punishments for fare evaders are intended to sting but not cut off a lifeline for the poor, and records of Christian's run-ins with TriMet show no sign of aggression until a day before the fatal knife attacks that left a city in shock.

A TriMet supervisor, police and medics were summoned May 25 after a man believed to be Christian caused a disturbance aboard one MAX train and then made threats while riding another.

Few details about the incident have been released. Neither the agency nor police have explained whether they considered any option that might have kept Christian off MAX the next day, when prosecutors say he stabbed three men who tried to defuse a racist diatribe directed at two teenage girls.

Even if unruly riders are temporarily barred from the system, not much would keep them from riding. TriMet's light-rail lines rely on the honor system, with only occasional and largely anonymous fare inspection.

TriMet has 61 transit cops, 15 security guards and 75 supervisors to patrol a light-rail system that runs hundreds of trips daily and a bus fleet that runs thousands more.

Though employees sometimes recognize problem riders, it's easy for them to blend into the sea of commuters.

"If your mission is to keep the guy off the transportation system, a fare checkpoint isn't going to do it," said Brian Michael Jenkins, national transportation safety and security director at the Mineta Transportation Institute in San Jose, California. "I need to have a human attendant at every access point. That's going to fundamentally change the system."

Such a system would be akin to the security setup at the nation's airports, and would add enormous cost and inconvenience to public transit, he said.

Christian's behavior before May 25 probably wouldn't have merited much attention from authorities - and certainly not a permanent ban.

That's by design. Under its own code, TriMet has no authority to ban riders for longer than six months.

That restriction is based on the philosophy that officials shouldn't deny access to public transportation for lengthy periods of time.

That policy may be changing, but not because of the recent attacks. Another glaring case is the notorious "TriMet barber."

Though Jared Weston Walter has been jailed repeatedly since 2009 for cutting or masturbating in women's hair aboard buses, the agency cannot banish him from the transit system.

In Walter's case, a court made avoiding TriMet a condition of his parole, keeping him off the system for a longer period.

But after his most recent arrest in April, TriMet spokeswoman Roberta Altstadt said the agency may ask its board to amend its code to allow for longer suspensions.

Though Christian has a lengthy criminal record, which includes convictions for robbery and kidnapping, none of it would not have kept him from the transit system. And records of his interactions with TriMet authorities didn't foreshadow the kind of outburst that preceded last Friday's fatal attack.

Starting in 2011, TriMet enforcement officials wrote up Christian -- under the name Jeremiah J. Christian -- for fare evasion at least eight times. Most were apparently fleeting encounters with no sign he became combative, records show.

In two cases, the charges were dismissed after he completed eight hours of community service. In four others, he was fined but never paid, and now owes nearly $1,500.

Altstadt said the transit agency doesn't track whether fines are paid; that falls to the court system.

In 2015, Christian was banned for 30 days after a Transit Police officer found him riding without a fare on a westbound Blue Line train. The officer made no notes about Christian's demeanor and didn't check boxes for "Threats" or "Harassment/Intimidation" -- descriptions that would have resulted in a 90-day exclusion.

People who end up committing violent acts in a public space often have earlier contacts with police or other authorities, said Jenkins, the transportation security researcher. But that doesn't necessarily mean those authorities could have anticipated the person posed threat.

"Dangerousness is extremely difficult to predict," Jenkins said. "A lot of people come on the radar in one form or another, and they haven't necessarily broken any laws that would indicate they pose an immediate threat to public safety."

It wasn't until last week that reports connected Christian to any disturbances on the transit system.

On May 25, he was involved in an altercation at the Interstate Rose Quarter MAX station, KGW-TV reported citing an unnamed source. Christian threw a plastic bottle at a woman, the station said, who pepper-sprayed him.

Altstadt said a Yellow Line train operator contacted dispatch to request a supervisor meet the train at the station, and that police and medics also responded. By the time officers arrived, however, the man was gone.

Shortly after, a cellphone video obtained by KOIN-TV showed a man believed to be Christian yelling derogatory statements about the driver of the train and threatening to stab someone.

That train's operator also put in a request for a supervisor, citing a "highly intoxicated" man who was yelling.

It's not clear what happened after that point, Altstadt said, because police have restricted TriMet's access to those records. Police confirmed they are aware of the altercation and the video.

Within 24 hours, Christian was in custody in connection with the train attack that killed Rick John Best, 53, of Happy Valley and Taliesin Myrddin Namkai-Meche, 23, of Southeast Portland, and seriously injured Micah David-Cole Fletcher, 21, of Southeast Portland.

He was arraigned Tuesday on two counts of aggravated murder, attempted aggravated murder and six other charges.

It remains to be seen whether the attacks bring about any changes in TriMet policy. Any changes in its approach to problem riders are fraught. In fact, authorities have recently moved in the opposite direction for fare evasion.

Where authorities have discretion to impose harsher penalties, data show, they have disproportionately affected minorities. A Portland State University study last year found that black MAX riders without fare were slightly more likely to be banned from the system than other groups -- even accounting for factors like repeat offenses.

The agency issued 5,900 exclusions from March 2014 to March 2016, mostly for fare evasion.

In January, metro-area district attorneys announced they would stop charging simple fare evaders with misdemeanors after evidence showed the criminal charge was more likely to be applied to minorities than white riders who committed the same offense.

-- Elliot Njus

enjus@oregonian.com

503-294-5034

@enjus