The police watchdog has begun an investigation into another four police officers as part of its inquiry into the sudden death of a man shortly after being released from custody. The Independent Office for Police Conduct (IOPC), which is investigating the contact South Wales police had with Mohamud Hassan during his arrest and time in custody, said it had served notices of investigation on three further South Wales officers and one custody detention officer. In addition, a police officer previously served had received an updated misconduct notice. The watchdog indicated that three officers were being investigated over their contact with Hassan during his time in custody at Cardiff Bay police station, and the other relates to officers who attended his home address at the time of his arrest. One of the notices includes an allegation of gross misconduct relating to honesty and integrity, including whether or not there were false or omitted entries made in custody logs concerning welfare checks made on Hassan. Other lines of inquiry relate to police officers’ use of force while escorting Hassan into the police station and the use of force while they were at his Cardiff home. IOPC director for Wales, Catrin Evans, said that in the course of an investigation, where an indication arises that an officer may have breached professional standards that may warrant a disciplinary sanction. “We serve a disciplinary notice to advise them they are subject to investigation,” she said. “We keep misconduct notices under review during the course of an investigation. At the conclusion the IOPC decides whether any officer under notice has a disciplinary case to answer.” The watchdog has previously indicated that Hassan could have suffered injuries during a large disturbance at his home the night before his death. More than 30,000 people have signed a petition calling on the watchdog to release documents and CCTV footage detailing the contact between officers and the 24-year-old on the evening of 8 January. Hassan, who was of Somali heritage, was arrested at his Cardiff home on a Friday evening on suspicion of breach of the peace. He arrived at the police station just after 10pm and was released without charge the following morning. Officers said he left custody at about 8.30am. He died later that day. Last month the Guardian revealed that Hassan had come into contact with dozens of police officers during his final hours. The IOPC subsequently said that while not all had direct contact or involvement with Hassan, they were gathering accounts from 46 officers and police staff who were on duty at Cardiff Bay police station over two shifts as well as those who were in supervisory positions. Two weeks earlier the watchdog said a police officer who accompanied Hassan to the police station in a van had been served a misconduct notice. The watchdog is investigating whether the officer failed to relay Hassan’s complaints of having a fit and being in pain when they arrived at Cardiff Bay police station.