Spain’s high court has launched an investigation into one of ETA’s most notorious members.
Inaki De Juana Chaos is suspected of breaking strict laws, which ban the praise of terrorism, following a demonstration in San Sebastian on Saturday.
He is alleged to have written a letter supporting terrorist action which was read out at the rally.
The police probe comes just two days after the ETA activist was released from jail. De Juana Chaos served 21 years for several offences, including the murder of 25 people in a string of car bombings in the 1980s.
Originally condemned to 3000 years imprisonment, he only served the maximum sentence of around 20 years under Spanish law.
The liberation has prompted outrage across Spain, with families of victims staging a protest against the early release.
The Spanish government has vowed to watch De Juana Chaos closely.