The Justice Department said Tuesday it was launching a federal civil rights investigation into the death of Freddie Gray, who died after suffering a severe spinal cord injury while in the custody of the Baltimore police.

Gray’s death has sparked repeated protests in Baltimore, where six police officers have been suspended as authorities there investigate what happened.

The Justice Department had been monitoring the situation in Baltimore and announced Tuesday afternoon that “based on preliminary information,” it was opening a probe to see if any civil rights violations occurred, a spokesperson said.

Authorities have called for calm in Baltimore, as the city became the latest flash-point in an ongoing national debate over how police officers use force, particularly toward black men and boys.

The city’s mayor and police commissioner said the results of an investigation would be given to prosecutors by May 1 to determine whether any criminal charges were warranted.

Details are still scarce on precisely what happened to Gray. A charging document said that Gray “was arrested without force or incident” on April 12. While he was able to talk and breathe when he  was placed into a transport van that morning, when he came out of the van “he could not talk, he could not breathe,” said Deputy Police Commissioner Jerry Rodriguez.