A man and woman have been arrested on suspicion of perverting the course of justice, as part of ongoing investigations into an, as yet, unresolved murder inquiry.

Kieran Williams, 18, went missing from his home in Sunderland on April 18 last year and, despite extensive inquiries to locate him, it was not until six weeks later, on May 31, that a police sniffer dog helped to locate a makeshift grave.

It was found on disused industrial land south of the River Wear, between the Northern Spire Bridge and Claxheugh Rocks.

Mr Williams’ body was found in the grave. He had been stabbed multiple times and set on fire.

Read more: Kieran Williams' death: Police say case remains 'open investigation'

Two men were later charged in connection with the death and stood trial at Newcastle Crown Court, where they were both acquitted of murder.

But, one of the pair, 20-year-old Louis Hackett, of Fordenbridge Square, Sunderland, was found guilty of manslaughter and jailed for five years.

The trial judge, Mr Justice Robert Jay, described it as, “an unusual case” and said he did not believe either defendant was, “the stabber”, or capable of inflicting wounds of that severity on someone they supposedly considered to be a friend.

But the judge said, in his view, the person who inflicted the fatal knife wounds remained at large.

He referred, specifically, to unidentified finger prints on soil in the makeshift grave and the fact that it was dug in such a neat way and left after being back-filled.

Read more: Kieran Williams murder trial: Louis Hackett guilty of manslaughter

Officers from Northumbria Police’ Major Investigation Team (MIT) continue to investigate Mr Williams’ killing, and today (August 1), arrested a 27-year-old woman and a 30-year-old man on suspicion of perverting the course of justice.

They were both said to remain in police custody.

A search of an address in the Ford Estate area of Sunderland has taken place and police remain in the area to carry out further inquiries and offer reassurance.

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The force said the investigation remains ongoing, and appealed to anyone with information about Mr William’s murder to contact police as soon as possible.

They are asked to do so, using the Northumbria Policer dedicated Major Incident Public Portal online, Public Portal (mipp.police.uk), or by calling 0191-437 4750, with voicemail available out-of-hours.

Alternatively, callers can make reports anonymously by ringing the independent charity, Crimestoppers, on (0800) 555111.