A Baltimore police officer was found not guilty Monday of criminal charges related to the death of 25-year-old Freddie Gray, an African-American man who died in police custody last year.

Here's what we know so far:

What happened to Freddie Gray?

Gray, a Baltimore resident, was arrested on April 12, 2015, on suspicion of carrying an illegal switchblade. It was later determined the knife was legal, according to PBS' NewsHour.

Although Gray repeatedly asked for help, paramedics were not called for 30 minutes.

He died one week later.

A medical examiner ruled Gray's death a homicide. His neck was broken in the back of a police transport van while he was handcuffed and shackled, but left unrestrained by a seat belt.

His death set off protests and rioting that month. Prosecutors announced on May 1, 2015, that six police officers had been charged in Gray's death.

What happened Monday?

Baltimore City Judge Barry Williams handed down a not guilty verdict Monday for Officer Edward Nero, who was charged with second-degree assault, misconduct in office and reckless endangerment.

Nero and Officer Garrett Miller chased down and handcuffed Gray after he fled from police, according to prosecutors.

Nero is the second officer to stand before a judge in Gray's death. In December, a judge declared a mistrial after a jury deliberating over the case of Officer William Porter was hung. Porter was charged with involuntary manslaughter, second-degree assault, misconduct in office and reckless endangerment. Prosecutors allege he ignored at least two of Gray's pleas for medical attention.

Who has been charged?

Six Baltimore police officers were charged with crimes ranging from murder to reckless endangerment. The other four officers face the following charges:

Officer Caesar Goodson Jr., driver of the police transport van:

  • Second-degree depraved heart murder
  • Manslaughter (involuntary)
  • Second-degree assault
  • Manslaughter by vehicle (gross negligence)
  • Manslaughter by vehicle (criminal negligence)
  • Misconduct in office
  • Reckless endangerment

Lt. Brian Rice

  • Manslaughter (involuntary)
  • Second-degree assault
  • Misconduct in office (two counts)
  • Reckless endangerment

Officer Garrett Miller

  • Second-degree assault
  • Misconduct in office (two counts)
  • Reckless endangerment

Sgt. Alicia White

  • Manslaughter (involuntary)
  • Second-degree assault
  • Misconduct in office
  • Reckless endangerment

How are people responding to the verdict?

A small group of protesters gathered outside the courtroom Monday, though they were outnumbered by reporters.

With last year's protests in mind, Baltimore Mayor Stephanie Rawlings-Blake asked for citizens to stay patient as the other trials continue.

"This is our American system of justice and police officers must be afforded the same justice system as every other citizen in this city, state and country," Rawlings-Blake said. "In the case of any disturbance in the city, we are prepared to respond. We will protect our neighborhoods, our businesses and the people of our city."

The Baltimore City Fraternal Order of Police greeted Nero's verdict with relief but lamented the arrests and upcoming trials as politically motivated and damaging to the officers.

"None of these officers did anything wrong," FOP president Lt. Gene Ryan said. "The State Attorney's Office responded to the riots and violence in Baltimore by rushing to charge these officers rashly and without any meaningful investigation. They seized a political opportunity and in the process destroyed six lives and demolished the relationship between the Baltimore police department and their own office."

What's next?

The Baltimore Police Department has launched an internal investigation into the events leading to Gray's death. Police spokesman T.J. Smith said Monday the investigations will continue until after the criminal cases go before a judge "because they (the officers) will likely be witnesses in each case."

Nero is currently on administrative duty, a position he'll hold until after the internal investigation is finished, Smith said.

Goodson will be the next officer to appear before a judge. He's scheduled in court on June 6, according to the Baltimore Sun. Rice will go to trial on July 5, Miller on July 27, Porter on Sept. 6 and White on Oct. 13.