Why it matters: The suspect was previously arrested in January and released on bail with conditions before being detained again by the Suffolk Constabulary's Major Investigation Team today.
The details: Officers discovered McNicholl's body at an address in Hawthorn Drive shortly before 18:00 on New Year's Day. A Home Office post-mortem revealed he died from head injuries and a single stab wound.
The suspect, who was 17 at the time of his initial arrest on 22 January, was also detained today on suspicion of being concerned in the supply of controlled drugs. He remains at Martlesham Police Investigation Centre.
The timeline: A number of arrests have been made during the investigation so far.
On 1 April, three men aged 17, 18, and 41 were arrested on suspicion of assisting an offender and drug supply offences. They were bailed to return on 1 October.
A woman in her 50s, previously arrested on suspicion of murder, has been told she faces no further action.
What's next: The 18-year-old suspect remains at Martlesham Police Investigation Centre for questioning on suspicion of murder and being concerned in the supply of controlled drugs.
Three other suspects are due to return to police on 1 October after being bailed in April.
Suffolk Constabulary continues to appeal for information about the case.
The bottom line: Police say they remain committed to securing justice for Mr McNicholl as the murder investigation enters its seventh month.
Anyone with information should contact police quoting reference 37/162/25 via the Major Incident Public Reporting Portal at https://mipp.police.uk/operation/363719P01-PO1, call 101, or contact Crimestoppers anonymously on 0800 555 111.
