Salim Allarakha Chaukiya, 24, a salesman at an electronics shop, was arrested on Thursday for allegedly stealing a police self-loading rifle (SLR) during the violence at Azad Maidan on August 11.
Chaukiya is the 24th person arrested in connection with the violence in which two people died and 54 were injured.
Chaukiya was arrested from Jogeshwari suburb and handed over to the Mumbai Police crime branch. On Wednesday, the crime branch had shown a documentary of suspects to staff of various police stations.
"He will be produced in court on Friday," said joint commissioner of police (crime) Himanshu Roy.
According to a police source, Chaukiya admitted to stealing the SLR.
"Chaukiya said he brandished the SLR during the mob frenzy, but threw the weapon and fled after the police regrouped," the source added.
Police suspect the stolen SLR is the one found broken after the riot. The SLR's magazine is missing.
Police are trying to ascertain if Chaukiya fired the weapon.
A mob had turned on the police and media at a rally held at the Azad Maidan to protest the killings of Muslims in Assam and Myanmar.