Demonstrators in Baltimore plan to shut down the city while holding one of their biggest protests to date as they demand justice for Freddie Gray, the man who died last Sunday after suffering a severe spinal cord injury while in police custody.

Gray, a 25-year-old black man, died of an unexplained spinal injury on April 19, exactly seven days after he was apprehended by Baltimore police. According to officials, Gray made eye contact with an officer and then fled the scene on the morning of Sunday, April 12. He was then chased by the officers, some of whom were patrolling the neighborhood on bike. Once they caught up to him, he was taken into custody for carrying a switchblade knife.

However, in cellphone footage captured by witnesses, Gray's legs appear to be limp as he was being dragged into a police van. Another witness at the scene said that Gray was screaming in pain, and that his legs folded like "origami."

"The officer had their knee in his neck. And he was just screaming -- screaming for life," said Kevin Moore, according to Vox. "He couldn't breathe. He needed an asthma pump, which he let them know. ... They ignored it."

Once police arrived at their destination, they discovered that Gray was unresponsive. He was then transported to the University of Maryland Medical Center's Shock Trauma Center, where he died one week later.

In wake of his death, the police union has released a statement suggesting that Gray's fatal injury occurred while he was riding in the police van. However, Baltimore residents are demanding details about exactly how and why Gray went into a coma immediately after he was brought into police custody. They are also calling for the arrests of the six officers who were involved in his arrest.

On Saturday, activists promised to hold a huge rally following a string of nationally covered protests in the past week. Protesters warned that they will "shut down" the city by marching through the streets and purposefully impeding traffic. The president of a black lawyers' group also predicted thousands of supporters would participate in the demonstration.

"Things will change on Saturday, and the struggle will be amplified," said Malik Shabazz of Black Lawyers for Justice, reports The Associated Press. "It cannot be business as usual with that man's spine broken, with his back broken, with no justice on the scene."

The planned demonstrations come a day after the Baltimore police department acknowledged that Gray did not receive medical attention early enough after being taken into custody, reports The Sun. The police union also admitted that Gray was not buckled into a seat when he was transported in a police van.

In the meantime, Maryland Gov. Larry Hogan and Baltimore Mayor Stephanie Rawlings-Blake on Friday asked the public to remain calm during the weekend protests. State troopers have also been called in for backup to maintain peace.