7 January 2013 Last updated at 08:54 ET

Jay Whiston murder: Facebook party death knife appeal

Caroline Shearer appealed to her son's killers to "be brave and come forward"

The sister of a teenager stabbed to death at a house party in Essex has called on those "shielding" the killer to come forward.

Jay Whiston, 17, died four months ago after he was attacked during a party organised via Facebook in Colchester.

Jay, from Clacton, would have turned 18 on Sunday. He died of a stab wound to the heart.

At a police press conference on Monday, Essex Police said it was looking for the murder weapon and a polo shirt.

Holly Fairburn, Jay's 25-year-old sister, said: "Please don't shield people that could devastate another family's lives as they have ours."

'Stood his ground'

Caroline Shearer, Jay's mother, 47, said: "Sunday would have been Jay's 18th birthday.

Police are searching for a T-shirt like this one which might have been worn by the killer

"If we could catch the person or people responsible, then at least justice would be done.

"It won't bring back my son, but we could all rest knowing that these people can't hurt anyone else."

Det Ch Insp Simon Parkes said police did not believe Jay was targeted on the night he died.

"When a fight broke out Jay stood his ground and tragically became the victim of mindless violence," he said.

Police are still searching for the knife used to kill Jay and a "distinctive" red-and-white polo T-shirt made by River Island.

Nine people have been arrested in connection with the case. Eight are currently on police bail until 22 March.

The ninth person - a 17-year-old boy - was released from police bail on Monday and told he faced no further action.