A 16-year-old girl from Colchester has been arrested on suspicion of conspiring to commit murder.
She is the fourth person to be arrested in connection with the stabbing of a 70-year-old man in Hythe Hill in the town in November.
This week detectives from Essex Police released a series of CCTV images in a bid to move on the investigation.
On Wednesday three men were detained in connection with the inquiry.
A Manningtree man, 49, and a Colchester man, 45, were arrested suspicion of conspiracy to commit murder, while a 20-year-old man from the Manningtree area was arrested on suspicion of attempted murder and conspiracy to commit murder.
Magistrates have given detectives more time to question them.
Investigators said the teenage girl arrested yesterday was awaiting questioning.
The victim was stabbed in the face, chest and back at about 5.40pm on Tuesday November 10, in the rear garden of his home in Hythe Hill.
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