Matthew Williams was found attacking Cerys Yemm, 22, at the Sirhowy Arms Hotel in Argoed on 6 November 2014.
He was Tasered four times by police and arrested but later died.
The Newport hearing was told he had previously made death and violence threats to his ex-girlfriend, probation service staff and a police officer.
PC Jake Silver, who deals with prolific offenders through Gwent Police's Integrated Offender Management section, said Williams' former partner received seven letters from him while he was locked up.
They contained threats of violence to her as well as threats towards a serving Detective Constable and the officer's wife and his children.
In the letters, Williams described sending a car "up in smoke" and described one person as a "dead man walking".
He described intending to serve his entire sentence - to negate the need to be on licence when released - so he could go "under the radar" when he was let out.
PC Silver said he believed Williams was "very capable of carrying out the threats" but said the Crown Prosecution Service decided there was not enough evidence to peruse the matter as Williams' ex girlfriend was not willing to be a witness.
PC Silver agreed there was a "lack of urgency" surrounding the letters because of an assumption Williams would remain in prison due to a pending court case, which later collapsed.
The inquest continues.
A man who killed woman at a hostel had sent letters threatening to kill others while in prison, an inquest has heard.