Harry Street pleaded guilty ahead of a trial at
Birmingham Crown Court
A killer who shot five people dead in 1978 has been told he might never be released from a secure hospital after "an arsenal" of weapons was found at his home last year.
Ex-Broadmoor patient Harry Street, 70, admitted making an improvised explosive device as well as 50 homemade bullets.
He was caught with the bomb, and three handguns at his Birmingham home.
At the city's crown court Mr Justice Blair sentenced Street to indefinite detention under the Mental Health Act.
He told Street, who entered guilty pleas ahead of his trial, it was necessary for the protection of the public he be subject to special restrictions which mean he may never be released.
West Midlands Police have started a serious case review but said there had been no trace of Street on their database. He was released in the mid 90s.
In 1978 Street shot three neighbours and a couple who ran a filling station.
George Burkitt and his wife Iris were shot in the head at the family's home in West Bromwich while their son Philip was shot in the chest.
He then drove to Stockingford, near Nuneaton, where he killed Michel and Lisa Di Maria, an Italian-born couple who ran a petrol station.
Street, originally called Barry Williams, pleaded guilty to the manslaughter of his victims on the grounds of diminished responsibility and was detained under mental health laws.
On Monday, the defendant, of Hazelville Road, Hall Green, admitted possessing the explosive device, and the prosecutors accepted his not guilty pleas to four other charges.
He had already pleaded guilty at previous hearings to three charges of possessing a prohibited firearm and a count of putting a neighbour in fear of violence between 2009 and 2013.
Sentencing, Mr Justice Blair said Street had begun to "become obsessed" with his neighbours from as early as 2007, and harboured delusions they were harassing him.
Harry Street was told he might never be released
"This was similar behaviour to that which had preceded the terrible events of 26th October 1978," he said.
However, he added "paranoid or delusional thinking on the defendant's part was not detected at that time".
Mr Justice Blair ordered his sentencing remarks to be made available to anyone involved in Street's care in future.
"I do so to record the narrow margin by which the risk of a further tragedy was averted," he said.
"The effect of these orders is that the defendant may never be released."
Det Ch Supt Kenny Bell of West Midlands Police said Street's previous identity only came to light after his harassment campaign "escalated" and a local officer made "extensive checks", which led to Street's GP.
Street moved several times after his release, and had spells at addresses in Shropshire, Kidderminster and Birmingham, he said.
The 2013 investigation found an "arsenal" of weapons at Harry Street's home in Hall Green
Harry Street shot five people dead on the same day in 1978, including three neighbours
He admitted manslaughter in 1979 and was detained under mental health laws
The explosive device and firearms were found at his home when he was arrested in connection with the allegations of harassment.
Prosecutor Michael Duck QC said the decision not to proceed with four of the charges - three counts of possession of prohibited firearms with intent to endanger life and one count of possession of ammunition with intent to endanger life - had been taken after consultation with witnesses.
He said lawyers had also taken into account the "overwhelming likelihood" Street would again be detained indefinitely in a secure hospital.
Harry Street - a timeline
"The Crown takes the view that the interests of the protection of the public are adequately served by acceptance of the (four not guilty) pleas," he said.
"It is quite apparent, and would have been the Crown's case, that this man commits offences of the utmost seriousness when he is mentally unwell.
"The overwhelming balance of medical opinion is that this is a significant problem that will take a very significant time to resolve, if it ever does."
Harry Street was detained in Broadmoor indefinitely after his killing spree but was allowed to move back to the Midlands with a new identity in 1994
Street, who is being treated at the high-security Ashworth Hospital on Merseyside, made the device between January and October last year.
He has admitted throwing items at neighbour Warren Smith's roof, banging on and drilling into walls late at night, making threats towards him and driving past his new address after he had moved out.