In a statement, the PJ said the motive for the crimes "is related to recurring disputes between groups living in different areas" in Braga.
The disputes resulted in mutual aggression, some of them using firearms.
On 6 July, the PJ conducted nine house searches, in the neighbourhoods of Enguardas and Picoto, and made five arrests.
The first incident occurred on 5 September, 2020, in Braga, with several gun shots at a group of people.
The other incidents date back to the early hours of 29 May this year, in the area of the bars around the University of Minho, in Braga, when a man was shot three times.
"In both cases, the shots did not cause the death of the victims by mere chance," the statement stresses.
During the searches, weapons, narcotics and mobile phones were seized.
Another man was also arrested on suspicion of drug trafficking.
"The Judicial Police is continuing with investigations to identify all those involved in the different incidents that occurred," the statement said.
The detainees, some of whom have criminal records, will be presented to the judicial authorities.
In April, the PJ had already arrested three other men, aged between 21 and 35, suspected of involvement in another dispute between the two rival groups.
In that case, were facts that occurred on 18 March, when "a group of at least three individuals provoked disturbances in the place and, faced with the reaction of the residents, took several shots with firearms towards the victims, not hitting them by mere chance".