About two weeks after he was released from prison, Freddie Johnson boarded a crowded subway train during morning rush hour in Manhattan, squeezed in behind a woman and ground his pelvis into her backside, authorities said.

It is a fairly common crime on subways in New York. But this was no common criminal.

Johnson has been arrested a staggering 53 times — the majority for groping women on the subway, police and prosecutors said.

In the latest incident, Johnson was being followed by plainclothes officers who recognized him from police photos, authorities said. He was charged with persistent sexual abuse, and if convicted this time, he could be sent away for life. The district attorney's office branded him a "recidivist transit grinder" at a court hearing earlier this week.

But the fact that Johnson was roaming the subways in the first place has raised questions about how the state deals with the problem of repeat sex offenders. His case even drew the scorn of a newspaper editorial this week that labeled Johnson the "Subway Rat."

His attorney, Afsi Khot, had no comment on the case, as is practice with Legal Aid attorneys.

Johnson, a registered sex offender, has been convicted at least twice of persistent sexual abuse within the last decade, prosecutors said. And he has a lengthy rap sheet, with 30 arrests for sex abuse, 13 for jostling and two for grand larceny, police said.

He was released from prison on March 25 after serving four years for persistent sexual abuse, according to correctional records. The state attorney general's office had argued that the 49-year-old should be confined under the state's civil commitment law for sex offenders, which went into effect last year, because he was at risk for repeat offenses.

But a Manhattan Supreme Court Judge disagreed and instead placed Johnson on strict court-ordered supervision and electronic monitoring.

Whether he should have been confined speaks to a larger issue about what authorities should do with criminals who are habitual offenders, but aren't violent.

Around half of all so-called exhibitionists like Johnson are repeat offenders, experts say. Exhibitionists have the highest rate of re-offense of all sex crimes, but there isn't much crossover into more egregious acts like rape or assault, said Elizabeth Jeglic, a professor of treatment and rehabilitation of offenders at John Jay College of Criminal Justice.

"Exhibitionism is disturbing, but in the larger scheme you want to commit the people who are grabbing kids off the street, or the rapist in Central Park," Jeglic said.

The goal of the Sex Offender Management and Treatment Act that went into effect last April is to protect society by keeping the most dangerous sex offenders off the streets and provide long-term treatment to ensure they don't repeat their crimes. To qualify, a criminal must have a "mental abnormality," and be "predisposed" to repeat the offense, prosecutors said.

Out of 1,299 sex offenders initially referred to the program in New York, 163 have been recommended for civil commitment, according to a report earlier this year by the state Office of Mental Health. Under the program, sex offenders are committed, treated, monitored and eventually discharged.

While it's painful for the victim no matter the crime, the system doesn't have room to deal with all offenders.

Currently, 10 percent of sex abuse cases are referred as possibilities for the program, on par with other states that have similar laws, the health department report said. It costs more than $100,000 per person per year to confine them. And there is currently bed space for 181 offenders at three facilities around the state. The development of 150 beds is under way, but it's obvious there will be shortfalls unless long-term projects are developed. Only 5 percent of those committed to the 19 other state programs in the country have been released.

Jeglic said New Jersey, where a similar law has been in place for about a decade, has run out of beds for offenders.

Either way, Johnson may end up behind bars for good if he's convicted in the latest incident, because the Manhattan district attorney's office said it will push for more serious punishment given his rap sheet. That means he could get up to life in prison. If he's convicted solely on the most recent charges, he could face four years.

A survey released last summer by the Manhattan borough president's office on sexual harassment in the subways found that 63 percent of those responding reported they were harassed in some way, whether it was random groping, lewd comments or unwanted advances. The report was compiled from 1,790 responses collected from New York City straphangers in all five boroughs.