Brother arrested in Milngavie New Year's Day fire probe
His partner Rebecca Williams, 24, was rescued from the house but remains in hospital, while his parents were treated for smoke inhalation.
Detectives launched a major investigation and said on Friday that they were “following a definite line of inquiry”.
A 26-year-old man, understood to be Blair Logan, has now been arrested over the incident.
He is due to appear at Glasgow Sheriff Court on Monday.
A Police Scotland spokesman said: “A 26-year-old man has been arrested and is currently detained in police custody in connection with the death of a 23-year-old man and the alleged attempted murder of a 24-year-old woman, a 54-year-old woman and a 54-year-old man on January 1 2017 in Achray Place, Milngavie.
“A report will be submitted to the Procurator Fiscal.”
Ms Williams, a broadcast journalist with Global Radio, was taken to the Queen Elizabeth University Hospital in Glasgow initially in a critical condition. She is now said to be in a stable condition.