Forensic experts are carrying out searches on three houses in the Gerald Corrigan murder hunt.
A 38 year-old man from Bryngwran is being held on suspicion of murder – and two men, a 48 year-old from Caergeiliog and a 36 year-old from Bryngwran, are being questioned on suspicion of conspiracy to kill and commit fraud.
Police say specialist officers are carrying out searches on three properties in the Caergeiliog and Bryngwran areas.
A fourth suspect, a 50 year-old woman, was arrested for suspected money laundering and fraud related offences during a series of morning raids on Tuesday.
Mr Corrigan, a former lecturer, died from his injuries at the Royal Stoke University Hospital on 11th May, just over three weeks after he was shot while fixing a satellite dish.
Detectives said they believe Mr Corrigan was deliberately targeted. More than 50 officers have been involved in the murder investigation over the past two months.
Detective Chief Superintendent Wayne Jones said: ”We are very grateful for the support and information provided by the community so far, but we are continuing to appeal to those who may have any information, no matter how insignificant they think it might be, to contact us.”
Anyone with information about the crossbow shooting should contact the major incident room at Llangefni CID on 101, quoting Operation Blue Fulgent, or Crimestoppers anonymously on 0800 555 111.