An Athens prosecutor ordered an investigation Monday into allegations of police brutality in the arrest of four alleged bank robbers, three of whom are suspected of being members of a domestic militant group, after relatives accused the police of torture and authorities released digitally altered mug shots that covered extensive bruising on three of the suspects.

The four men, aged 20 to 24, were arrested Friday in northern Greece shortly after a double bank robbery in a village near the city of Kozani. Four other people are being sought in that case, in which two banks were robbed simultaneously. Three of those arrested are suspected of being linked to a militant group that has claimed responsibility for a series of bombings.

Police released mug shots over the weekend seeking further information on the suspects from the public. All four photos appeared to have been digitally altered, with signs of bruising showing through the alteration on the left side of three suspects' faces — bruising that was clear in photos taken during their transfer from the local police station.

There have been numerous allegations of brutality while in Greek police custody in recent years, with suspects complaining of beatings and humiliations during detentions and arrests.