SERVES THE RED, PURPLE, AND YELLOW LINES AS WELL AS BUSES. THIS INCIDENT JUST A DAY AFTER A DEADLY MASS SHOOTING ON A BLUE LINE TRAIN. THE SUSPECT NOW CHARGED WITH THE MURDERS OF FOUR PEOPLE. HE WILL BE IN COURT FOR THE FIRST TIME TOMORROW. TONIGHT, THE COOK COUNTY STATES ATTORNEY: THE LABOR DAY SHOOTING A "RANDOM ATTACK" AS INVESTIGATORS STILL DON'T KNOW THE MOTIVE. POLICE, CITY, AND CTA LEADERS UPDATED THEIR INVESTIGATION INTO 30-YEAR-OLD KARA WELSH THREE. SARAH. >> Reporter: OFFICIAL STOPPED SHORT OF SAYING THESE VICTIMS WERE HOMELESS BUT THEY ACKNOWLEDGE THEY WERE ASLEEP ON THE TRAIN AT THE TIME OF THIS ATTACK . TALKING ABOUT THE MANY LAYERS OF CONCERN FOR ANYONE WHO USES THE TRAIN. THIS IS THE FIRST TIME TONIGHT WHEN WE HEARD FROM THE CTA PRESIDENT DORVAL R. CARTER PUBLICLY SINCE THESE KILLINGS. >> IT IS HORRIFIC. WE WANT ANSWERS. RIGHT NOW, WE DON'T HAVE ANSWERS TO WHY ANYONE WOULD ENGAGE IN SUCH A HEINOUS ACT. >> Reporter: ANSWERS ABOUT MOTIVE, COOK COUNTY STATES ATTORNEY KIM FOX SAID, MAY NEVER COME, EVEN AS THE PROSECUTOR'S OFFICE PREPARES TO TAKE THE SUSPECT TO COURT WEDNESDAY. >> IT IS SAFE TO SAY THIS WAS A RANDOM ATTACK. >> Reporter: 30-YEAR-OLD KARA WELSH THREE FACING FOUR FIRST-DEGREE MURDER COMES. DAVIS HAS BEEN ARRESTED SEVERAL TIMES SINCE 2014. THAT YEAR, HE WAS SENTENCED TO TWO YEARS PROBATION FOR A MISDEMEANOR BATTERY CHARGE AND PLEADED GUILTY TO DISORDERLY CONDUCT IN 2020. INVESTIGATORS REVEALING THE GLOCK 43 THEY FOUND WHEN TAKING THE WITH INTO CUSTODY. THE CALIFORNIA PINK PLATFORM IS A FORENSIC MATCH TO THE SHELL CASINGS FOUND ACROSS TWO CARS AT THE BLUE LINE FOURTH STOP. INVESTIGATORS TELL ME THEY BELIEVE DAVIS STARTED SHOOTING NEAR THE HARLEM STATION, ONE-STOP, WEARING A MASK AT THE TIME. THE MEDICAL EXAMINER'S OFFICE IDENTIFYING VICTIMS AS 28-YEAR-OLD SIMEON BIHESI, 60-YEAR-OLD ADRIAN COLLINS. THE 64-YEAR-OLD WOMAN AND A 52-YEAR-OLD MAN. >> DEALING WITH CRIME ON THE CTA IS A COMPLEX ISSUE THAT INVOLVES MULTIPLE LAYERS OF SECURITY AND POLICE RESOURCES. >> Reporter: CTA PRESIDENT DORVAL R. CARTER SAID TO USE THE STRENGTHS OF CAMERA NETWORK, ADDING THE NEW AI GUN RECOGNITION SOFTWARE, LAUNCHED LAST WEEK, DID NOT PLAY A ROLE IN THE MANHUNT. THAT SOFTWARE ONLY SCANS FOR FIREARMS ON PLATFORMS AND CARTER SAID ANY DECISION TO EXPAND TO TRAINS WOULD COME AFTER THE PILOT IS CONCLUDED. IN JUST THE LAST HOUR, WE LEARNED THAT 64-YEAR-OLD WOMAN HAS BEEN IDENTIFIED AS MARGARET MILLER. AUTHORITIES TELLING US THEY ARE STILL TRYING TO FIND NEXT OF KIN FOR THE FOURTH VICTIM. WE KNOW THAT KARA WELSH THREE WILL BE IN COURT TOMORROW AT NOON. PROSECUTORS SECOND, AT THAT TIME, THEY