Why was he even set free? MPs demand answers on killer Harry Street

And the former MP who represented the area where Street, originally called Barry Williams, said he could not believe how the man was allowed to live 'a tram ride away' from where he first opened fire.

They are concerned that he was freed 20 years ago - just over 15 years after his merciless killing spree that started by gunning down his neighbours on the Bustleholme Mill housing estate in West Bromwich.

Questions being asked of the Government include how the 70-year-old was able to 'slip through the net' when it came to monitoring him after his release.

But they are also seeking answers as to why he was even let out of Broadmoor in the first place, having been detained there indefinitely when he was sentenced.

Street was detained under mental health laws in 1979 for the manslaughter of his three neighbours and a couple who ran a filling station in Warwickshire.

Tom Watson, MP for West Bromwich East, whose constituency covers the Bustleholme Mill estate, said: "I am deeply shocked and extremely concerned to hear of this case.

"Clearly Mr Street has slipped through the net of the criminal justice system when it comes to monitoring people who have committed violent crimes with mental illness.

"It will be deeply worrying for local people in West Bromwich and I will be writing to ministers to demand that they examine this case with the utmost urgency."

His predecessor Lord Snape, who as Peter Snape was MP for West Bromwich East at the time of the killings, wrote to the Government in 1994 to call Street's release 'crass, insensitive and dangerous' after he was found to be living in a bail hostel just six miles away.

Lord Snape said: "Some people came to see me at a surgery at the town hall and said he had been released.

"I wrote a letter about it and got assurances back that he would not be allowed to be anywhere near West Bromwich.

"Now it turns out he was a tram ride away from where he killed his neighbours and displaying the same sort of behaviour as in the run up to the killings.

"It is remarkable that he was freed in the first place.

"He was in Broadmoor for only 15 years - that's three years for each of the people he killed.

"Somebody is responsible for that decision, for allowing him out against the wishes of the people of West Bromwich at the time, for allowing him to change his name and despite assurances live just a few miles away from where he killed people."

And Ian Austin, a member of the influential Home Affairs Select Committee, said he would be seeking an explanation from Home Secretary Theresa May.

The Labour MP for Dudley North said: "It is unbelievable.

"Harry Street's original crimes were committed in 1978 yet he was released from Broadmoor within 20 years.

"I will be raising this with the Home Secretary and the Ministry of Justice.

"People will want to know how he came to be free and in a position to have firearms and an improvised explosive device.

"He's pleaded guilty to crimes between 2009 and 2013 - that's five years ago.

"He clearly still presents a danger to the public. Why was he released from Broadmoor in the first place?"