She's 66 years old with soft, white hair cut in a bob and the appearance of a genial grandmother but Marilyn Jean Hartman has built up quite a collection of mugshots.
Nicknamed the "serial stowaway" for her history of unticketed jaunts on commercial flights, she has reappeared in the news after allegedly landing in London earlier this month without a passport or boarding pass.
More recently she has also landed back in jail on charges of misdemeanor criminal trespass and violation of bail bond, after breaching bail by visiting Chicago's O'Hare International Airport -- from where she is said to have departed for the UK in the first place.
Her image may be familiar to airport and police cameras but just how she manages to board planes and make trips remains a mystery, as does her personal life and background.
Little to nothing is known about whether she has or had a family and an employment history, where she is from and how or why she started her unauthorized travels.
How does she do it?
Reporters who have followed her arrests said the success of her evasive maneuvers depends on her ability to blend into a crowd as a seemingly harmless, elderly white woman.
She employs tactics like ducking under ropes, keeping her head down, piggybacking on small groups, and using other passengers' discarded boarding passes, Joe Eskenazi wrote in The Guardian last week.
After one court appearance in 2014, Hartman refused to give details regarding how she was able to slip through security.
"I don't think it's wise to say how I got through. I don't want to help the enemy," she said then.
Where does she go?
Hartman has been arrested numerous times for trying to sneak aboard airlines and staying in places without authorization.
Hartman made national news in 2014, when she was arrested at Los Angeles International Airport for successfully having slipped aboard a flight from Mineta San Jose International Airport in San Jose, California, without a ticket. She pleaded no contest to the charges and was sentenced to probation.
"I want to go with a paid ticket. ... I want to do everything legal," Hartman said outside the courthouse. "It was clearly wrong on my part. ... It was stupid and it is something I don't want to repeat."The next day she was rearrested at Los Angeles International Airport.
In August the same year, she had two run-ins with authorities at Sky Harbor Airport in Phoenix. On August 14, Hartman was given a warning for trying to enter a security checkpoint without a ticket. Twelve days later, she was arrested in an airport terminal for criminal trespass. A day after that, Hartman was again seen loitering around a security checkpoint, Phoenix police said.
She was arrested again in Florida in 2015 after authorities said she was staying in a hotel room that had been booked by someone else.
Why does she do it?
In 2016 the Chicago Police Department described Hartman as "a habitual trespasser and stowaway" after she was arrested at O'Hare for violating her probation, which barred her from setting foot on airport property.
She was sentenced to six months of house arrest in a mental health facility for violating court orders to stay away from airports, CNN affiliate WBBM reported.
Hartman has been ordered to undergo a psychiatric evaluation after her more recent alleged trip to London, CNN affiliate WLS reported.
WLS said that Hartman told reporters after her 2014 arrest that she suffered from mental illness and had been diagnosed with depression. She had previously said that she had been homeless and felt safer in airports than on the street, it said.
"My sense is that there is a compulsive quality to her actions," WLS quoted Northwestern Medicine Psychologist Mark Reinecke as saying.
"It's repetitive. It's planful, and even when she's been warned not do this, in some ways she can't resist the impulse or the desire to engage in it," Reinecke told the station. "It's not about consequences and rewards in the traditional sense, it's about the meaning this has in her life."
Can she be stopped?
Aside from revealing flaws in airport security, Eskenazi said that Hartman's case has revealed the justice system's inability to deal with someone like her. In a 2015 profile for San Francisco Magazine, Eskenazi described a revolving door of arrests, court appearances, and lenient sentences with no end in sight and no clear rationale for her actions.
"Marilyn Jean Hartman's life is in a holding pattern," he wrote. "She just wants to fly. Period. And she'll try again, and again, and again, until she's grounded. For good."
Woman's most recent arrest is in Chicago
Her life, motives are a mystery