Greater Manchester Police is being investigated into how the force dealt with a domestic incident at a house in Oldham, which was later the scene of a 26-hour hostage situation.
In the early hours of 25 July, police were called following reports of a man armed with a gun holding a woman and two children hostage inside a house on Pemberton Way in Shaw, Oldham.
The children, aged one and six, were soon released from the property unharmed, but the standoff with police involving suspect Marc Schofield continued for nearly 24 more hours.
Police eventually entered the house just before 5am on 26 July and safely removed the woman, named locally as 27-year-old Lisa Hurley, and arrested Schofield on suspicion of making threats to kill and false imprisonment.
Prior to the siege taking place, police were called to the same house after receiving reports of concerns for the welfare of a woman. After dealing with the incident, Schofield is then suspected to have returned to the home around two hours later to lock himself and the others inside.
The Independent Police Complaints Commission (IPCC) is now investigating the police response to the domestic incident prior to the hostage situation.
IPCC Commission Delegate Catherine Bates said: "Our independent investigation is in its very early stages.
"We will look at the police response to the initial report of a domestic incident and the actions of officers involved in dealing with this report.
"We are aware of the substantial press coverage around this matter and the events that unfolded. We have carefully considered the referral from Greater Manchester Police and have decided to investigate this independently; this is common when an incident has resulted in serious injuries, and where there appears to have been prior police contact."
Schofield is due to appear at Manchester Minshull Street Crown Court on two counts of section 18 wounding, possession of an imitation firearm with intent to cause fear or serious violence and false imprisonment.