BALTIMORE — Protesters who’ve been holding near-daily demonstrations this week over the death of Freddie Gray are promising their biggest march yet a day after the Baltimore Police Department acknowledged that it failed to get him the medical attention he needed after his arrest.

Protesters vowed to “shut down” the city by marching through the streets and snarling traffic. The president of a black lawyers’ group predicted thousands of people would turn out for the demonstration, when good weather is forecast and the Baltimore Orioles host the Boston Red Sox.

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

Shabazz has demanded the arrest of six officers involved in the arrest of Gray, who died Sunday, a week after suffering a spinal injury while in police custody.

The officers are suspended with pay and under criminal investigation by their own department. The U.S. Justice Department is reviewing the case for any civil rights violations, and Gray’s family is conducting their own probe.