Police consider the case of a teenager found dead in a makeshift grave as, “an open investigation”, following the manslaughter conviction of a former friend.

The Northumbria force is “actively pursuing a number of lines of inquiry” into the still unresolved killing of Kieran Williams, in Sunderland.

It is in the wake of the jailing of 20-year-old Louis Michael Hackett after he was convicted at Newcastle Crown Court of manslaughter, following a trial in January.

Hackett, of Fordenbridge Square, and his 19-year-old co-accused, Ben Cook, of Fordfield Road, both Sunderland, were both, however, acquitted of Mr Williams’ murder.

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

Mr Cook was also cleared of manslaughter by the jury.

Hackett was said to have lured Mr Williams to the scene of his death, on waste ground near the new Northern Spire Bridge, in Sunderland, on April 18 (Easter Monday) last year.

The court heard that Mr Williams was repeatedly stabbed and placed in a pre-dug grave, before attempts were made to set fire to his body.

It was almost six weeks later that a police dog handler came across the grave, covered with sticks and leaves, on disused former industrial land on the southern side of the River Wear.

Forensic examination confirmed Mr Hackett’s fingerprints were found on clay used to backfill the grave, although other unidentified prints were also revealed.

Mr Williams died from stab wounds to the chest, one of which damaged the aorta.

Addressing Hackett's sentencing hearing, at the court, on Monday (March 27), the trial judge, Mr Justice Robert Jay, described it as having been, “an unusual case.”

But he said: “I don't believe either of these young men were the stabber. It was someone else."

The judge told Hackett: "You were not Kieran's murderer.

“It's difficult to be sure what happened that evening, but certain hard facts are clear.

“Kieran was one of your best friends. He trusted you completely."

The judge said he believed Hackett persuaded Mr Williams to meet him at the mini “Clatchy” rocks, not far from the grave site, as they often went there to smoke cannabis, and he would have known something, “untoward” was to happen.

But he said he would not have known that he would suffer really serious harm, less so that he would be stabbed 23 times in what the judge described as, “a brutal attack.”

Read more: Kieran Williams trial: Closing speeches in Sunderland murder case

Mr Justice Jay said: "The jury clearly didn't think Ben Cook was the stabber either.

“I would endorse that conclusion.

"The better view is someone else is the stabber and he has still not been apprehended.

“I say that because my assessment of the evidence is neither of you was capable of an attack of this severity, particularly against a close friend.

"I also bear in mind the undetected print or prints and the neat way the grave was constructed and then left after being filled in.

“Neither of you were capable of doing that.

"The unattributed prints remain a mystery. At least one other person left the grave in the tidy condition it was found."

The judge said both accused told the jury, “a complete pack of lies", telling Hackett he did so out of a need to protect himself and, “out of fear."

He said: "You were not aware a partly dug grave would be awaiting him.

“Had you been aware of the grave you would be guilty of murder."

The judge said Hackett sought to blame Mr Cook for the stabbing after being confronted with the evidence of his fingerprint in the clay in the grave.

But he said: "You acted under the instruction of another or others in filling in the grave."

He imposed a sentence of five years in a youth offenders’ institution on Hackett.

The judge said the real perpetrator or perpetrators may have, “got away with it”, stating that in this case, “justice has not been done.”

But he added that it also would not be done if the defendant received a sentence of more than five years.

Speaking after the sentencing hearing, Detective Chief Inspector Matt Steel, of Northumbria Police, said: “Our thoughts continue to be with Kieran’s family and loved ones following their loss.

"This is a truly tragic case in which a family have been left completely devastated and we will continue to support them wherever we can.

Read next:

Kieran Williams murder: Evidence of one of accused Sunderland killers

Accused duo were at scene of alleged Sunderland murder, jury told

Phone evidence outlined to trial jury over death of Sunderland teen

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“We want to make it clear that violence of any kind is completely unacceptable and is never the answer.

"When incidents do occur we are committed to doing all we can to bring those responsible to justice by putting them before the court.

“We can confirm this remains an open investigation and we are actively pursuing a number of lines of inquiry, and we will also continue to act on any new information which comes forward.”