A 27-year-old man recently released from prison was arrested Monday for a knife attack on two sisters at an Oakland BART station which left one dead.   Brendan Weber of NBC Bary Area reports that witnesses and surveillance video identified John Cowell as the attacker, and police recovered the possible murder weapon at a nearby construction site. Cowell was released from prison last May after serving time for a 2016 armed robbery.  At that time he was on probation for battery and drug convictions, considered "low level" crimes under California law.  While the attack has rocked the community, it is the third murder at a BART station in five days.  The day before the knife attack a 47-year-old man hit the ground after being punched in the face at a BART station, leaving him brain dead.