Cambridgeshire Police are linking the suspect in a mass-stabbing on a high-speed train to three knife-related incidents in Peterborough in the 24 hours beforehand.
The force has referred itself to the watchdog.
32-year-old Anthony Williams has appeared in court charged with attempted murder on the LNER service on Saturday evening.
He’s also accused of attacking someone at a station in east London early that morning.
Shadow Home Secretary and MP for Croydon South, Chris Philp, says the government should be making use of technology available.
