A 45-year-old man wrote threatening letters and cards to fellow residents in a Kidderminster block of flats, Worcester Crown Court was told.
Duncan Moseley smeared his own blood on some of the anonymous correspondence, however, and was tracked down through his DNA, said prosecutor Andrew Wilkins.
Moseley, now of no fixed address, pleaded guilty to two offences of putting persons in fear of violence. He was given a nine-month jail sentence suspended for two years.
Judge Michael Cullum also ordered him to attend six sessions of an anger management course. He made a restraining order forbidding Moseley from contacting one of his victims, a 78-year-old woman living alone.
David Howarth, for Moseley, said he had no previous convictions but had been examined by a psychiatrist. He had been diagnosed as suffering from autism and obesssive, compulsive behaviour. His condition had deteriorated when social worker support was withdrawn.
The case had lost him his flat and he was now living in bed and breakfast accommodation.
The judge said last Friday that Moseley's conduct had not only distressed a vulnerable woman but had also put neighbours under suspicion. It had been a campaign which had led to an innocent man being arrested for a short time but the judge realised there was concern over Moseley's mental health.