About millions of black suspects, and white suspects too. Black suspects in particularly might see it as a useful way to call out to their community for help.

People who can't breathe, as a byproduct of the not breathing, also can't say "I can't breathe". People who are having moderate difficulty breathing might reasonably cry out that they can't breathe, since that's an understandable panic response. People who can breathe just fine also might falsely cry out that they can't breathe. Suspects lie about how they're being treated, and how they are responding. Police lie about how they are being treated, and what the suspect is doing. In his initial report, the cop who executed Daniel Shaver claimed that Mr. Shaver moved forward to gain a better firing position on the police. He did not say "Mr. Shaver, weeping and drunk, crawled forward because my commanding officer on the scene ordered him to, and when he fell and put his hand near his waistband, I put 5 AR-15 rounds into him."

I'm glad everyone's walking around with camera nowadays.