A 15-year-old boy has been arrested on suspicion of murder after a former Royal Navy officer was run over by his own car.
The boy, who is also held on suspicion of burglary, is the fourth person to be arrested over the death of Mike Samwell in Chorlton, Manchester, in the early hours of 23 April.
A 29-year-old from south Manchester arrested on Wednesday remains in custody.
Two men, aged 20 and 21, have been released on bail pending further enquiries.
Mr Samwell had gone outside to confront intruders who had entered his house while he and his wife were asleep.
He was knocked down as his Audi S3 was driven away.
The 37-year-old, who spent 12 years in the Royal Navy, was pronounced dead at hospital about an hour later.
Detective Inspector Lewis Hughes, of Greater Manchester Police's major incident team, said: "This has been a fast-moving investigation and we have made significant progress since Mike's murder.
"However, our enquiries do not end there and we will continue to move forward with the investigation but we still need the public's help.
"If you have any information that you believe can help us then I would urge you to please contact police immediately."
:: Anyone with any information is asked to contact police on 0161 856 9908, or alternatively call 101 or the independent charity Crimestoppers on 0800 555 111.