Four people have now been arrested in connection with the death of Mike Samwell.
A 15-year-old boy is being questioned on suspicion of murder after an ex-Royal Navy officer was run down and killed by car thieves.
The youth from south Manchester was arrested on Thursday morning and is also being questioned in custody on suspicion of burglary.
He is the fourth person to be arrested in connection with the death of Mike Samwell, 35, from Chorlton, Manchester, in the early hours of Sunday April 23.
A 29-year-old man from south Manchester remains in custody after he was arrested on Wednesday night on suspicion of murder and burglary.
Two men aged 20 and 21 who were arrested on suspicion of murder have been bailed pending further enquiries.
Mr Samwell had been chasing intruders from his £500,000 home in Chorlton, Manchester, who broke in while he and his wife Jess were asleep upstairs. He went outside and was run down as the thieves sped off in his Audi S3 car.
His wife screamed his name and cried for help as he lay dying in the street before neighbours dashed to the scene and an ambulance was called.
Mr Samwell, who served 12 years in the Royal Navy, was pronounced dead in hospital around 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 and have now arrested two more people who will be questioned by detectives.
“However, our inquiries do not end there and we will continue to move forward with the investigation but we still need the public’s help.”
Mr Samwell graduated from the University of Leeds before working in a number of roles for the Royal Navy, including on board a nuclear attack submarine as a weapons officer.
Since leaving the forces he had worked as a programme manager for engineering firm Atkins in Warrington, Cheshire.
In a tribute, his family said: “Mike’s death has made a huge hole in our lives that can never be filled.
“Mike was the most wonderful husband, brother and son. He would do anything for anyone and was an ever dependable and generous family member and friend to so many.”