From BBC news,

"I heard a load of noise, people saying, 'Get out, get down'!

"I saw an Asian guy run onto the train hotly pursued by three plain-clothes police officers."

"One of them was carrying a black handgun - it looked like an automatic - they pushed him to the floor, bundled on top of him and unloaded five shots into him."

"I saw the gun being fired five times into the guy - he's dead."

This has just happened.