(CNN)The arrest and death of Freddie Gray in Baltimore has stoked protests and accusations of police brutality. But it's unclear how Gray, arrested on a weapons charge April 12, suffered a severe spinal cord injury that led to his death seven days later. Here are the big questions surrounding this explosive case: . Gray's arrest . What we know: Gray was arrested on a weapons charge in a high-crime area of Baltimore known for drugs. He "gave up without the use of force," according to  Baltimore Deputy Police Commissioner Jerry Rodriguez. An officer apparently took his Taser out, and was prepared to use it on Gray, but he never deployed it, Rodriguez said, and none of the six officers involved in the arrest describe using force against the 25-year-old. Gray was placed inside a police van and was able to talk, said Rodriguez who described Gray as upset. "And when Mr. Gray was taken out of that van, he could not talk, and he could not breathe," according to Rodriguez. What we don't know: It's unknown what caused the spinal cord injury that led to his death a week after the arrest, and it's also unknown what, if anything, happened inside the van. The knife . What we know: Court documents allege that Baltimore Police Department Officer Garrett Miller arrested Gray after finding a switchblade in his pocket. The Gray family attorney called the allegation a "sideshow." Gray was carrying a "pocket knife of legal size," attorney William Murphy told CNN. Police never saw the knife and chased Gray only after he ran from them, the attorney said. The court documents also say that Gray "fled unprovoked upon noticing police presence." "The officer noticed a knife clipped to the inside of his front right pants pocket. The defendant was arrested without force or incident," the documents say. "The knife was recovered by this officer and found to be a spring assisted, one-hand-operated knife." Maryland law makes it illegal to "wear or carry a dangerous weapon of any kind concealed on or about the person," including switchblades. What we don't know: It's not clear that simply having a knife is a crime, said Baltimore Mayor Stephanie Rawlings-Blake. "It is not necessarily probable cause to chase someone. So, we still have questions," she said. What can be seen on the released video . What we know: Segments of cell phone video shot from two different positions appear to begin after Gray has been arrested and show officers dragging Gray, who is handcuffed, to a van. He can be heard screaming. "He was dragged a bit," said Rawlings-Blake, "but then you see him using his legs to get into the van, so he was able-bodied when he was in the van, and we know that when he was finally taken out of the van, he was unresponsive." Officers placed more restraints on Gray inside the van, police said, while surveillance video recorded him conscious and talking. That was at 8:54 a.m. At 9:24 a.m., police called an ambulance for Gray. Police say Gray requested medical attention, including an inhaler, and an ambulance later took him to the University of Maryland Medical Center's Shock Trauma Center. What we don't know: It's unknown why Gray screamed, and the video doesn't capture the entire incident, start to end. It's unclear what happened between 8:54 a.m. and 9:24 a.m. Police response . What we know: In the wake of Gray's death, six police officers have been suspended. Their names were released Tuesday, a standard procedure after an "in-custody death," said Baltimore Police Department spokesman Capt. Eric Kowalczyk. It doesn't mean the officers did anything wrong or that they were the only officers involved, he said. They are: Lt. Brian Rice, 41, who joined the department in 1997; Officer Caesar Goodson, 45, who joined in 1999; Sgt. Alicia White, 30, who joined in 2010; Officer William Porter, 25, who joined in 2012; Officer Garrett Miller, 26, who joined in 2012; and Officer Edward Nero, 29, who joined in 2012. Police Commissioner Anthony Batts said that authorities plan to conclude their investigation by May 1. Their findings will go to the state's attorney's office, where prosecutors will decide whether charges should be filed. What we don't know: The officers say they didn't use force against Gray, but that's not certain. Gray's past run-ins with authorities . What we know: According to court documents CNN obtained, there were more than 20 criminal court cases in Maryland against Gray, and five of those cases were still active at the time of his death. The cases involve mostly drug-related charges, but there are charges from March for second-degree assault and destruction of property. Gray was due in court on a possession charge on April 24. He had been in and out of prison since 2009 for various drug cases, said Maryland Department of Corrections spokesman Gerard Shields. In February 2009, he was sentenced to four years in prison for two counts of drug possession with intent to deliver. Shields said he could not determine from records what kind of drug was involved. Gray was paroled on June 30, 2011. On April 4, 2012, Gray was arrested for violating parole but he didn't go back to prison, Shields said, reasoning that  whatever Gray allegedly did, it "was something minor." Gray went back to prison again in May 2013 for drug possession and served a month. He was released in June. What we don't know: It's not known whether Gray's criminal past had anything to do with his arrest, or his death. CNN's AnneClaire Stapleton, Stephanie Gallman and Eliott C. McLaughlin, Dana Ford and Ben Brumfield contributed to this report.
Gray was arrested on a weapons charge April 12; he was dead seven days later .
Gray was placed inside a police van after his arrest; it's unclear if anything happened inside the van .
Gray has a criminal history but it's unclear whether that had anything to do with his arrest, or death .