Sana-ul-Haq Hussain, the accused, was arrested this morning, a senior police officer said.
Zia-ul-Haq Hussain, his elder brother, was found shot dead near Milan hotel in Dharavi yesterday afternoon.
"After identifying the victim, we questioned his relatives and learnt that Sana-ul-Haq had come to Mumbai, but hadn't visited his brothers," said the officer.
Police got suspicious as Sana didn't turn up to visit the family even after the brother's death.
He was arrested at Kalyan station when he was on the way to Bihar, police said.
The duo had a tiff with Zia over a payment, and in a fit of rage Sana shot his brother dead, police said.
His friend was absconding. Further probe was on.