By Austin Carter

MIAMI (CBSMiami) –  A homeless man arrested in Miami, accused of killing Ryan Rogers, an innocent teen in Palm Beach County, could have been sentenced to two decades in prison for a past crime.

With a past littered with violent offenses, how was he still on the streets?

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Between 2004 and 2016, Semmie Williams faced at least a dozen criminal charges spanning three states, including several charges in Florida.

“I would describe it as an innocent child victim having a chance encounter with a very violent criminal,” said Chief Clint Shannon, Palm Beach Gardens Police Department.

CBS4 News obtained court documents from one of Williams’ prior violent crimes in 2014 – aggravated assault with strangulation and battery on a senior citizen in Georgia.

According to documents, the offenses had a possible maximum sentence of 21 years.

Fulton County prosecutors wanted to keep Williams behind bars saying that the attack was unprovoked, and if Williams was allowed to leave their custody it was “basically just exporting a potentially violent situation to another jurisdiction.”

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“Unfortunately for the young man who was killed in South Florida, a lot of what goes into a judge’s mind in determining what kind of sentence is imposed is what the defendant’s prior criminal history is,” said David Weinstein.

Williams’ history had no felony charges.

Former state and federal prosecutor David Weinstein says that key piece may have led to the judge’s sentencing, releasing Williams from custody on time served and giving him first-offender status.

“If this individual had accumulated a number of felony convictions he would not have been eligible for a first offender kind of sentence and so he would have been sentenced to a longer number of years, and if there were a number of felony convictions, the judge would in all likelihood have sentenced him to a number of years much closer to what the maximum punishment was,” says Weinstein.

Documents also show that Williams was originally sentenced to be banished from Fulton County, Georgia, and be put on a bus to Florida to stay with his mom.

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She later changed her tune and was unwilling to take him back.