Why it matters: This marks the second arrest in the investigation of McNicholl's death, which has prompted an extensive police operation including specialist dive teams.
The big picture: McNicholl, 63, was found dead at his home in Hawthorn Drive on 1 January. A post-mortem examination revealed he died from head injuries and a stab wound.
Latest developments:
The teenage suspect was taken to Martlesham Police Investigation Centre on Wednesday 22 January for questioning
Specialist dive teams conducted searches in the River Orwell near Princes Street on Tuesday 21 January
A woman in her 50s, previously arrested on suspicion of murder, remains on bail until 9 April
What's next: Suffolk Constabulary's Major Investigation Team continues to lead the inquiry and is appealing for witnesses to come forward.
Bottom line: Police are urging anyone with information to contact them via their Major Incident Public Reporting Portal or by calling 101, quoting reference 37/162/25. Anonymous reports can be made to Crimestoppers.
