Prison authorities were warned that the suspected terrorist who went on a bloody rampage in the Belgian city of Liege was radicalised before he killed two policewomen and a passerby while on a temporary release pass from jail.

Belgian media reported that a guard informed prison bosses on Saturday, two days before the killings, that Benjamin Herman, 31, was spending too much time with a suspected Islamic State of Iraq and Levant (Isil) recruiter and a childhood friend of one of the 2016 Brussels bombers. Herman was released on Monday and struck in the heart of Belgium’s third city on Tuesday.

ISIL has claimed responsibility for the “lone wolf” attack, which ended with the black-clad pistol-toting killer taking a hostage at a high school before being gunned down in a hail of 26 police bullets, but provided no proof. Belgian prosecutors have opened a terror investigation.

State security and police already had files on Herman. While prison authorities may not have been aware of those before granted him a two-day release as part of his rehabilitation, there were several guards’ reports warning he was radicalised, as well as a service assessment that he was “ultra-violent”.

The latest guard report warned that Herman had fallen under the influence of the dangerous and notorious prisoner, who is not due to be released until 2040.